Form N-Q

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, DC 20549

FORM N-Q


QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number         811-6623         

        Nuveen California Select Tax-Free Income Portfolio         
(Exact name of registrant as specified in charter)


        333 West Wacker Drive, Chicago, Illinois 60606         
(Address of principal executive offices) (Zip code)


Jessica R. Droeger—Vice President and Secretary
        333 West Wacker Drive, Chicago, Illinois 60606         
(Name and address of agent for service)

Registrant's telephone number, including area code:         312-917-7700        

Date of fiscal year end:            3/31          

Date of reporting period:         6/30/06         

Form N-Q is to be used by management investment companies, other than small business investment companies registered on Form N-5 (§§ 239.24 and 274.5 of this chapter), to file reports with the Commission, not later than 60 days after the close of the first and third fiscal quarters, pursuant to rule 30b1-5 under the Investment Company Act of 1940 (17 CFR 270.30b1-5). The Commission may use the information provided on Form N-Q in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-Q, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-Q unless the Form displays a currently valid Office of Management and Budget (“OMB”) control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to the Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609. The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. § 3507.

Item 1. Schedule of Investments

    Portfolio of Investments (Unaudited)             
    Nuveen California Select Tax-Free Income Portfolio (NXC)             
    June 30, 2006             
Principal        Optional Call         
Amount (000)    Description    Provisions (1)    Ratings (2)    Value 
    Consumer Staples – 2.1%             
$             235    California County Tobacco Securitization Agency, Tobacco Settlement Asset-Backed Bonds, Sonoma    6/15 at 100.00    BBB   $   226,307 
     County Tobacco Securitization Corporation, Series 2005, 4.250%, 6/01/21             
1,620    California County Tobacco Securitization Agency, Tobacco Settlement Asset-Backed Revenue    6/12 at 100.00    BBB    1,632,555 
     Bonds, Fresno County Tobacco Funding Corporation, Series 2002, 5.625%, 6/01/23             
1,855    Total Consumer Staples            1,858,862 
    Education and Civic Organizations – 9.4%             
1,000    California Educational Facilities Authority, Revenue Bonds, Stanford University, Series 1999P,    12/09 at 101.00    AAA    1,026,410 
     5.000%, 12/01/23             
45    California Educational Facilities Authority, Revenue Bonds, University of Redlands, Series    10/15 at 100.00    A3    44,825 
     2005A, 5.000%, 10/01/35             
1,000    California Educational Facilities Authority, Revenue Bonds, University of San Diego, Series    10/12 at 100.00    A2    1,049,180 
     2002A, 5.500%, 10/01/32             
    California Educational Facilities Authority, Revenue Bonds, University of the Pacific,             
    Series 2006:             
35     5.000%, 11/01/21    11/15 at 100.00    A2    35,930 
45     5.000%, 11/01/25    11/15 at 100.00    A2    45,753 
3,000    California Infrastructure Economic Development Bank, Revenue Bonds, J. David Gladstone    10/11 at 101.00    A–    3,140,070 
     Institutes, Series 2001, 5.500%, 10/01/19             
2,000    California State Public Works Board, Lease Revenue Bonds, University of California, UCLA    10/12 at 100.00    AAA    2,050,000 
     Replacement Hospital Project, Series 2002A, 5.000%, 10/01/22 – FSA Insured             
1,000    Long Beach Bond Financing Authority, California, Lease Revenue Refunding Bonds, Long Beach    11/11 at 101.00    AAA    1,035,590 
     Aquarium of the South Pacific, Series 2001, 5.250%, 11/01/30 – AMBAC Insured             
8,125    Total Education and Civic Organizations            8,427,758 
    Health Care – 10.9%             
335    California Health Facilities Financing Authority, Revenue Bonds, Cedars-Sinai Medical Center,    11/15 at 100.00    A3    335,379 
     Series 2005, 5.000%, 11/15/34             
2,000    California Infrastructure Economic Development Bank, Revenue Bonds, Kaiser Hospital Assistance    8/11 at 102.00    A+    2,080,700 
     LLC, Series 2001A, 5.550%, 8/01/31             
1,500    California Statewide Community Development Authority, Hospital Revenue Bonds, Monterey    6/13 at 100.00    AAA    1,576,665 
     Peninsula Hospital, Series 2003B, 5.250%, 6/01/18 – FSA Insured             
1,500    California Statewide Community Development Authority, Insured Mortgage Hospital Revenue Bonds,    11/09 at 102.00    A    1,545,060 
     Mission Community Hospital, Series 2001, 5.375%, 11/01/26             
90    California Statewide Community Development Authority, Revenue Bonds, Daughters of Charity    7/15 at 100.00    BBB+    91,648 
     Health System, Series 2005A, 5.250%, 7/01/24             
1,515    California Statewide Community Development Authority, Revenue Bonds, Kaiser Permanante System,    3/16 at 100.00    A+    1,500,108 
     Series 2006, 5.000%, 3/01/41             
1,880    California Statewide Community Development Authority, Revenue Bonds, Los Angeles Orthopaedic    6/07 at 101.00    AAA    1,923,691 
     Hospital Foundation, Series 2000, 5.500%, 6/01/17 – AMBAC Insured             
790    Central California Joint Powers Health Finance Authority, Certificates of Participation,    8/06 at 100.00    Baa2    774,611 
     Community Hospitals of Central California, Series 1993, 5.000%, 2/01/23             
9,610    Total Health Care            9,827,862 
    Housing/Multifamily – 0.9%             
750    California Statewide Community Development Authority, Student Housing Revenue Bonds, EAH –    8/12 at 100.00    A    775,350 
     Irvine East Campus Apartments, LLC Project, Series 2002A, 5.500%, 8/01/22 – ACA Insured             
    Industrials – 2.0%             
1,250    California Pollution Control Financing Authority, Solid Waste Disposal Revenue Bonds, Republic    No Opt. Call    BBB+    1,289,525 
     Services Inc., Series 2002C, 5.250%, 6/01/23 (Mandatory put 12/01/17) (Alternative Minimum Tax)             
500    California Pollution Control Financing Authority, Solid Waste Disposal Revenue Bonds, Waste    1/16 at 102.00    BBB    498,930 
     Management Inc., Series 2002A, 5.000%, 1/01/22 (Alternative Minimum Tax)             
1,750    Total Industrials            1,788,455 
    Long-Term Care – 1.7%             
1,500    ABAG Finance Authority for Non-Profit Corporations, California, Insured Senior Living Revenue    11/12 at 100.00    A    1,537,245 
     Bonds, Odd Fellows Home of California, Series 2003A, 5.200%, 11/15/22             
    Tax Obligation/General – 19.9%             
500    California, General Obligation Bonds, Series 2003, 5.250%, 11/01/19 – RAAI Insured    11/13 at 100.00    AA    527,620 
    California, General Obligation Bonds, Series 2004:             
750     5.000%, 2/01/23    2/14 at 100.00    A    768,758 
800     5.125%, 4/01/25    4/14 at 100.00    A    824,176 
1,000     5.125%, 2/01/27    2/14 at 100.00    A    1,024,570 
2,000    Fremont Unified School District, Alameda County, California, General Obligation Bonds, Series    8/12 at 101.00    AAA    2,063,700 
     2002A, 5.000%, 8/01/21 – FGIC Insured             
    Golden West Schools Financing Authority, California, General Obligation Revenue Refunding             
    Bonds, School District Program, Series 1999A:             
4,650     0.000%, 8/01/16 – MBIA Insured    No Opt. Call    AAA    2,930,570 
1,750     0.000%, 2/01/17 – MBIA Insured    No Opt. Call    AAA    1,070,178 
2,375     0.000%, 8/01/17 – MBIA Insured    No Opt. Call    AAA    1,419,039 
2,345     0.000%, 2/01/18 – MBIA Insured    No Opt. Call    AAA    1,358,130 
    Mountain View-Los Altos Union High School District, Santa Clara County, California, General             
    Obligation Capital Appreciation Bonds, Series 1995C:             
1,015     0.000%, 5/01/17 – MBIA Insured    No Opt. Call    AAA    613,537 
1,080     0.000%, 5/01/18 – MBIA Insured    No Opt. Call    AAA    618,170 
    Oakland Unified School District, Alameda County, California, General Obligation Bonds,             
    Series 2005:             
130     5.000%, 8/01/25 – MBIA Insured    8/15 at 100.00    AAA    133,675 
135     5.000%, 8/01/26 – MBIA Insured    8/15 at 100.00    AAA    138,615 
1,500    San Diego Unified School District, San Diego County, California, General Obligation Bonds,    7/13 at 101.00    AAA    1,604,505 
     Series 2003E, 5.250%, 7/01/24 – FSA Insured             
150    San Jose-Evergreen Community College District, Santa Clara County, California, General    9/15 at 100.00    AAA    154,155 
     Obligation Bonds, Series 2005A, 5.000%, 9/01/27 – MBIA Insured             
2,565    Sunnyvale School District, Santa Clara County, California, General Obligation Bonds, Series    9/15 at 100.00    AAA    2,641,847 
     2005A, 5.000%, 9/01/26 – FSA Insured             
22,745    Total Tax Obligation/General            17,891,245 
    Tax Obligation/Limited – 17.5%             
1,000    Bell Community Redevelopment Agency, California, Tax Allocation Bonds, Bell Project Area,    10/13 at 100.00    AA    1,057,160 
     Series 2003, 5.625%, 10/01/33 – RAAI Insured             
3,500    California State Public Works Board, Lease Revenue Bonds, Department of Corrections,    No Opt. Call    AAA    4,053,245 
     Calipatria State Prison, Series 1991A, 6.500%, 9/01/17 – MBIA Insured             
1,000    California State Public Works Board, Lease Revenue Bonds, Department of Mental Health,    6/14 at 100.00    A–    1,067,680 
     Coalinga State Hospital, Series 2004A, 5.500%, 6/01/23             
660    California, Economic Recovery Revenue Bonds, Series 2004A, 5.000%, 7/01/15    7/14 at 100.00    AA–    698,564 
120    Capistrano Unified School District, Orange County, California, Special Tax Bonds, Community    9/15 at 100.00    AAA    123,595 
     Facilities District, Series 2005, 5.000%, 9/01/24 – FGIC Insured             
1,000    Fontana Public Financing Authority, California, Tax Allocation Revenue Bonds, North Fontana    10/15 at 100.00    AAA    1,016,070 
     Redevelopment Project, Series 2005A, 5.000%, 10/01/32 – AMBAC Insured             
90    Hesperia Community Redevelopment Agency, California, Tax Allocation Bonds, Series 2005A,    9/15 at 100.00    AAA    93,038 
     5.000%, 9/01/20 – XLCA Insured             
    Irvine, California, Unified School District, Community Facilities District Special Tax Bonds,             
    Series 2006A:             
60     5.000%, 9/01/26    9/06 at 103.00    N/R    59,581 
135     5.125%, 9/01/36    9/06 at 103.00    N/R    132,750 
215    Los Angeles Community Redevelopment Agency, California, Lease Revenue Bonds, Manchester Social    9/15 at 100.00    Aaa    217,795 
     Services Project, Series 2005, 5.000%, 9/01/37 – AMBAC Insured             
1,300    Orange County, California, Special Tax Bonds, Community Facilities District 03-1 of Ladera    8/12 at 101.00    N/R    1,358,812 
     Ranch, Series 2004A, 5.625%, 8/15/34             
105    Rialto Redevelopment Agency, California, Tax Allocation Bonds, Merged Project Area, Series    9/15 at 100.00    AAA    106,420 
     2005A, 5.000%, 9/01/35 – XLCA Insured             
605    Sacramento City Financing Authority, California, Lease Revenue Refunding Bonds, Series 1993A,    No Opt. Call    AAA    658,415 
     5.400%, 11/01/20 – MBIA Insured             
3,000    San Mateo County Transit District, California, Sales Tax Revenue Bonds, Series 2005A, 5.000%,    6/15 at 100.00    AAA    3,110,220 
     6/01/21 – MBIA Insured             
1,000    Santa Clara County Board of Education, California, Certificates of Participation, Series 2002,    4/12 at 101.00    AAA    1,020,300 
     5.000%, 4/01/25 – MBIA Insured             
1,000    Travis Unified School District, Solano County, California, Certificates of Participation,    9/16 at 100.00    Aaa    1,022,750 
     Series 2006, 5.000%, 9/01/26 – FGIC Insured             
14,790    Total Tax Obligation/Limited            15,796,395 
    Transportation – 8.2%             
1,150    Foothill/Eastern Transportation Corridor Agency, California, Toll Road Revenue Bonds, Series    1/10 at 100.00    BBB–    1,103,805 
     1995A, 5.000%, 1/01/35             
5,000    Los Angeles Harbors Department, California, Revenue Refunding Bonds, Series 2001B, 5.500%,    8/11 at 100.00    AAA    5,270,097 
     8/01/17 – AMBAC Insured (Alternative Minimum Tax)             
1,000    Port of Oakland, California, Revenue Bonds, Series 2002M, 5.250%, 11/01/20 – FGIC Insured    11/12 at 100.00    AAA    1,055,040 
7,150    Total Transportation            7,428,942 
    U.S. Guaranteed – 16.5% (3)             
400    Beverly Hills Unified School District, Los Angeles County, California, General Obligation    8/12 at 100.00    AA (3)    423,888 
     Bonds, Series 2002A, 5.000%, 8/01/26 (Pre-refunded 8/01/12)             
    California Department of Water Resources, Power Supply Revenue Bonds, Series 2002A:             
2,000     5.750%, 5/01/17 (Pre-refunded 5/01/12)    5/12 at 101.00    Aaa    2,209,740 
2,000     5.125%, 5/01/19 (Pre-refunded 5/01/12)    5/12 at 101.00    Aaa    2,145,020 
750    California Educational Facilities Authority, Revenue Bonds, Pepperdine University, Series    8/09 at 100.00    A1 (3)    785,925 
     2002A, 5.500%, 8/01/32 (Pre-refunded 8/01/09)             
2,600    California Educational Facilities Authority, Revenue Bonds, University of the Pacific, Series    11/11 at 100.00    A2 (3)    2,765,542 
     2002, 5.250%, 11/01/21 (Pre-refunded 11/01/11)             
1,400    Golden State Tobacco Securitization Corporation, California, Enhanced Tobacco Settlement    6/13 at 100.00    AAA    1,518,580 
     Asset-Backed Bonds, Series 2003B, 5.500%, 6/01/33 (Pre-refunded 6/01/13)             
2,800    Los Angeles, California, Wastewater System Revenue Bonds, Series 1998A, 5.000%, 6/01/23    6/08 at 101.00    AAA    2,890,636 
     (Pre-refunded 6/01/08) – FGIC Insured             
2,000    North Orange County Community College District, California, General Obligation Bonds, Series    8/12 at 101.00    AAA    2,127,420 
     2002A, 5.000%, 8/01/22 (Pre-refunded 8/01/12) – MBIA Insured             
13,950    Total U.S. Guaranteed            14,866,751 
    Utilities – 1.9%             
200    Los Angeles Department of Water and Power, California, Power System Revenue Bonds, Series    7/13 at 100.00    AAA    206,314 
     2003A-2, 5.000%, 7/01/21 – MBIA Insured             
215    Merced Irrigation District, California, Electric System Revenue Bonds, Series 2005, 5.125%,    9/15 at 100.00    AAA    220,521 
     9/01/31 – XLCA Insured             
1,225    Turlock Irrigation District, California, Revenue Refunding Bonds, Series 1992A, 6.250%,    No Opt. Call    Aaa    1,323,515 
     1/01/12 – MBIA Insured             
1,640    Total Utilities            1,750,350 
    Water and Sewer – 5.1%             
2,160    California Statewide Community Development Authority, Water and Wastewater Revenue Bonds,    10/11 at 101.00    AAA    2,250,763 
     Pooled Financing Program, Series 2001B, 5.125%, 10/01/22 – FSA Insured             
150    Healdsburg Public Financing Authority, California, Wastewater Revenue Bonds, Series 2006,    4/16 at 100.00    AAA    153,183 
     5.000%, 4/01/36 – MBIA Insured             
325    Los Angeles Department of Water and Power, California, Waterworks Revenue Bonds, Series    7/16 at 100.00    AAA    334,672 
     2006A-2, 5.000%, 7/01/27 – AMBAC Insured             
825    South Feather Water and Power Agency, California, Water Revenue Certificates of Participation,    4/13 at 100.00    BBB    839,405 
     Solar Photovoltaic Project, Series 2003, 5.375%, 4/01/24             
1,000    Woodbridge Irrigation District, California, Certificates of Participation, Water Systems    7/13 at 100.00    BBB+    1,021,910 
     Project, Series 2003, 5.625%, 7/01/43             
4,460    Total Water and Sewer            4,599,933 
$        88,325    Total Long-Term Investments (cost $83,653,562) – 96.1%            86,549,148 
    Short-Term Investments – 2.4%             
2,150    Puerto Rico Government Development Bank, Adjustable Refunding Bonds, Variable Rate Demand        A-1+    2,150,000 
     Obligations, Series 1985, 2.250%, 12/01/15 – MBIA Insured (4)             
2,150    Total Short-Term Investments (cost $2,150,000)        2,150,000 
$        90,475    Total Investments (cost $85,803,562) – 98.5%        88,699,148 
    Other Assets Less Liabilities – 1.5%            1,384,552 
    Net Assets – 100%       $  90,083,700 

(1)    Optional Call Provisions: Dates (month and year) and prices of the earliest optional call or 
    redemption. There may be other call provisions at varying prices at later dates. Certain 
    mortgage-backed securities may be subject to periodic principal paydowns. 
(2)    Ratings: Using the higher of Standard & Poor's or Moody's rating. Ratings below BBB by Standard 
    & Poor's Group or Baa by Moody's Investor Service, Inc. are considered to be below investment grade. 
(3)    Backed by an escrow or trust containing sufficient U.S. Government or U.S. Government agency 
    securities which ensure the timely payment of principal and interest. Such investments are 
    normally considered to be equivalent to AAA rated securities. 
(4)    Investment has a maturity of more than one year, but has variable rate and demand features 
    which qualify it as a short-term investment. The rate disclosed is that in effect at the end of the 
    reporting period. This rate changes periodically based on market conditions or a specified market index. 
N/R    Not rated. 

Income Tax Information

The following information is presented on an income tax basis. Differences between amounts for financial statement and federal income tax purposes are primarily due to the treatment of paydown gains and losses, timing differences in recognizing taxable market discount and timing differences in recognizing certain gains and losses on investment transactions.

At June 30, 2006, the cost of investments was $85,802,392.

Gross unrealized appreciation and gross unrealized depreciation of investments at June 30, 2006, were as follows:

Gross unrealized:     
  Appreciation    $3,147,886 
  Depreciation    (251,130) 
Net unrealized appreciation (depreciation) of investments    $2,896,756 

Item 2. Controls and Procedures.

  1. The registrant's principal executive and principal financial officers, or persons performing similar functions, have concluded that the registrant's disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the "1940 Act") (17 CFR 270.30a-3(c))) are effective, as of a date within 90 days of the filing date of this report that includes the disclosure required by this paragraph, based on their evaluation of the controls and procedures required by Rule 30a-3(b) under the 1940 Act (17 CFR 270.30a-3(b)) and Rule 13a-15(b) or 15d-15(b) under the Securities Exchange Act of 1934 (17 CFR 240.13a-15(b) or 240.15d-15(b)).
  2. There were no changes in the registrant's internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act (17 CFR 270.30a-3(d)) that occurred during the registrant's last fiscal quarter that have materially affected, or are reasonably likely to materially affect, the registrant's internal control over financial reporting.

Item 3. Exhibits.

File as exhibits as part of this Form a separate certification for each principal executive officer and principal financial officer of the registrant as required by Rule 30a-2(a) under the 1940 Act (17 CFR 270.30a-2(a)), exactly as set forth below: EX-99 CERT Attached hereto.


SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant)         Nuveen California Select Tax-Free Income Portfolio        

By (Signature and Title)*          /s/ Jessica R. Droeger                     
                                                    Jessica R. Droeger
                                                    Vice President and Secretary

Date         August 28, 2006        

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)*         /s/ Gifford R. Zimmerman                    
                                                   Gifford R. Zimmerman
                                                   Chief Administrative Officer (principal executive officer) 

Date         August 28, 2006        

By (Signature and Title)*         /s/ Stephen D. Foy                              
                                                   Stephen D. Foy
                                                   Vice President and Controller (principal financial officer) 

Date        August 28, 2006        

* Print the name and title of each signing officer under his or her signature.