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            AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON
                                 APRIL 26, 2006

                          REGISTRATION NO. 333-125739

               (INVESTMENT COMPANY ACT REGISTRATION NO. 811-07024)

                                 ---------------

                     U.S. SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                 ---------------

                                    FORM N-14

                                 ---------------

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                                 ---------------

                         PRE-EFFECTIVE AMENDMENT NO. ___

                       [X] POST-EFFECTIVE AMENDMENT NO. 1

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                        (CHECK APPROPRIATE BOX OR BOXES)

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                          COLUMBIA FUNDS SERIES TRUST I

                              ONE FINANCIAL CENTER

                           BOSTON, MASSACHUSETTS 02111

                                 1-800-426-3750

                                 ---------------

                           R. SCOTT HENDERSON, ESQUIRE

                         COLUMBIA MANAGEMENT GROUP, LLC
                              ONE FINANCIAL CENTER
                           BOSTON, MASSACHUSETTS 02111
                     (NAME AND ADDRESS OF AGENT FOR SERVICE)

                                 ---------------

                                   COPIES TO:
                            BRIAN D. MCCABE, ESQUIRE
                                ROPES & GRAY LLP
                             ONE INTERNATIONAL PLACE
                           BOSTON, MASSACHUSETTS 02110

                            CAMERON S. AVERY, ESQUIRE
                             BELL, BOYD & LLOYD LLC
                       70 WEST MADISON STREET, SUITE 3300
                             CHICAGO, IL 60602-4207

It is proposed that this filing will become effective immediately upon filing
pursuant to paragraph (d) of Rule 462 under the Securities Act of 1933, as
amended.

There have been no changes to the proxy statement/prospectus or statement of
additional information as filed with the Registrant's Registration Statement on
Form N-14 (File No. 333-125739), as filed by the Registrant's predecessor,
Columbia Funds Trust IV, with the Commission on June 10, 2005 (Accession No.
0000950135-05-003247).

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PART C.   OTHER INFORMATION

ITEM 15.  INDEMNIFICATION

Incorporated by reference to Item 25 of Post-Effective Amendment No. 71 to the
Registrant's Registration Statement on Form N-1A under the Securities Act of
1933 and the Investment Company Act of 1940 (File No. 002-41251).

ITEM 16. EXHIBITS

    (1)(a)      Amendment No. 4 to the Agreement and Declaration of Trust dated
                November 15, 1991, incorporated by reference to Post-Effective
                Amendment No. 46, filed with the Commission via EDGAR on or
                about July 31, 1997.

    (1)(b)      Amendment No. 5 to the Agreement and Declaration of Trust dated
                April 1, 1999, incorporated by reference to Post-Effective
                Amendment No. 54 filed with the Commission via EDGAR on or about
                May 26, 1999.

    (1)(c)      Amendment No. 6 to the Amended and Restated Agreement and
                Declaration of Trust dated January 26, 2001, incorporated by
                reference to Post-Effective Amendment No. 61 filed with the
                Commission via EDGAR on or about March 28, 2001.

    (1)(d)      Amendment No. 6 to the Agreement and Declaration of Trust dated
                October 13, 2003, incorporated by reference to Post-Effective
                Amendment No. 67 filed with the Commission via EDGAR on or about
                October 28, 2003.

    (1)(e)      Form of Second Amended and Restated Declaration of Trust dated
                __________, 2005, incorporated by reference to Exhibit 1(e) in
                Part C, Item 16 of the Registrant's Registration Statement on
                Form N-14 (File No. 333-125739), as filed with the Commission on
                June 10, 2005 (Accession No. 0000950135-05-003247).

    (2)(a)      By-Laws of Registrant as amended and restated August 20, 2004,
                incorporated by reference to Post-Effective Amendment No. 71
                filed with the Commission via EDGAR on or about January 28,
                2005.

    (2)(b)      Form of Bylaws amended and restated effective ________, 2005,
                incorporated by reference to Exhibit 2(b) in Part C, Item 16 of
                the Registrant's Registration Statement on Form N-14 (File No.
                333-125739), as filed with the Commission on June 10, 2005
                (Accession No. 0000950135-05-003247).

    (3)         Not Applicable

    (4)         Agreement and Plan of Reorganization, dated as of June 1, 2005
                between Columbia Funds Trust IV, on behalf of its Columbia
                Tax-Exempt Fund series, and Columbia Funds Trust IX , on behalf
                of its Columbia Managed Municipals Fund and Columbia Management
                Advisors, Inc. -- incorporated by reference to Appendix A to
                Part A of the Registrant's Registration Statement on Form N-14
                (File No. 333-125739), as filed with the Commission on June 10,
                2005 (Accession No. 0000950135-05-003247).

    (5)(a)      Form of Specimen of Share Certificate -- incorporated by
                reference to Exhibit 4 in Part C, item 24(b) of Post-Effective
                Amendment No. 45 to the Registration Statement on Form N-1A of
                Columbia Funds Trust IV (file Nos. 2-62492 and 811-2865) filed
                with the Commission on or about March 21, 1997.

    (5)(b)      Article III, Section 4, Article V, Section 1, Article VIII,
                Section 4 and Article IX Sections 1 and 7 of the Declaration of
                Trust as amended and Sections 2.1, 2.3 and 2.5 of the By-Laws,
                each define the rights of shareholders.

    (6)(a)      Management Agreement between Registrant and Columbia Management
                Advisors, Inc. dated November 1, 2003 - Incorporated by
                reference to Post-Effective Amendment No. 71 filed with the
                Commission via EDGAR on or about March 29, 2004.



    (6)(b)      Sub-Advisory Agreement between Registrant, Columbia Management
                Advisors, Inc. and Stein Roe Investment Counsel LLC dated
                November 1, 2003 - Incorporated by reference to Post-Effective
                Amendment No. 74 filed with the Commission via EDGAR on or about
                March 1, 2004.

    (6)(c)      Amendment to the Investment Management Agreement between the
                Registrant and Columbia Management Advisors, Inc. executed as of
                October 12, 2004.

    (7)(a)      Distribution Agreement between the Registrant and Columbia Funds
                Distributor, Inc. (formerly named Liberty Funds Distributor,
                Inc.) dated April 30, 1999 -- incorporated by reference to
                Exhibit (e)(1) in Part C, Item 23 of Post-Effective Amendment
                No. 131 to the Registration Statement on Form N-1A of Columbia
                Funds Trust III (File Nos. 2-15184 and 811-881), filed with the
                Commission on or about January 28, 2004.

    (7)(b)      Appendix 1 to the Distribution Agreement between the Registrant
                and Columbia Funds Distributor, Inc. (formerly named Liberty
                Funds Distributor, Inc.) dated November 1, 2003 -- incorporated
                by reference to Exhibit (e)(2) in Part C, Item 23 of
                Post-Effective Amendment No. 131 to the Registration Statement
                on Form N-1A of Columbia Funds Trust III (File Nos. 2-15184 and
                811-881), filed with the Commission on or about January 28,
                2004.

    (7)(c)      12b-1 Plan Implementing Agreement between the Registrant and
                Columbia Funds Distributor, Inc.( formerly known as Liberty
                Funds Distributor, Inc.) -- incorporated by reference to Exhibit
                (k)(7) in Part C, Item 24(2) of Post-Effective Amendment No. 5
                to the Registration Statement on Form N-2 of Columbia Floating
                Rate Advantage Fund (File Nos. 333-51788 and 811-09709), filed
                with the Commission on or about December 17, 2003.

    (7)(d)      Appendix 1 to the 12b-1 Plan Implementing Agreement between the
                Registrant and Columbia Funds Distributor, Inc. (formerly known
                as Liberty Funds Distributor, Inc.) -- incorporated by reference
                to Exhibit (k)(8) in Part C, Item 24(2) of Post-Effective
                Amendment No. 5 to the Registration Statement on Form N-2 of
                Columbia Floating Rate Advantage Fund (File Nos. 333-51788 and
                811-09709), filed with the Commission on or about December 17,
                2003.

    (7)(e)      Form of Selling Agreement with Columbia Funds Distributor, Inc.
                (formerly known as Liberty Funds Distributor, Inc.) --
                Incorporated by reference to Post-Effective Amendment No. 49
                filed with the Commission via EDGAR on November 20, 1998.

    (7)(f)      Form of Asset Retention Agreement -- incorporated by reference
                to Exhibit 6(d) in Part C, Item 24(b) of Post-Effective
                Amendment No. 10 to the Registration Statement on Form N-1A of
                Columbia Funds Trust VI (filed under former name Liberty Funds
                Trust VI) (File Nos. 33-45117 and 811-6529), filed with the
                Commission on or about September 27, 1996.

    (8)         Not Applicable

    (9)(a)      Custodian Contract between Registrant and State Street Bank and
                Trust Company dated October 24, 2001 -- incorporated by
                reference to Exhibit (g) in Part C, Item 23(b) of Post-Effective
                Amendment No. 56 to the Registration Statement on Form N-1A of
                Columbia Funds Trust II (filed under former name Liberty Funds
                Trust II) (File Nos. 2-66976 and 811-3009), filed with the
                Commission on or about October 26, 2001.

    (9)(b)      Appendix A to the Custodian Contract between Registrant and
                State Street Bank and Trust Company -- Incorporated by reference
                to Exhibit (j)(2) in Part C, Item 24(2) of Post-Effective
                Amendment No. 6 to the Registration Statement on Form N-2 of
                Columbia Floating Rate Fund (File Nos. 333-51466 and 811-08953),
                filed with the Commission on or about December 17, 2003.

    (10)(a)     Rule 12b-1 Plan dated July 1, 2001 and amended and restated on
                July 1, 2002, November 4, 2002, November 1, 2003 and May 11,
                2004 -- incorporated by reference to Exhibit (m)(1) in Part C,
                Item 23(b) of Post-Effective Amendment No. 64 to the
                Registration Statement on Form N-1A of Columbia Funds Trust II
                (File Nos. 2-66976 and 811-3009), filed with the Commission on
                or about July 27, 2004.



    (10)(b)     Appendix 1 to Rule 12b-1 Distribution Plan dated May 11, 2004 --
                incorporated by reference to Exhibit (m)(2) in Part C, Item
                23(b) of Post-Effective Amendment No. 64 to the Registration
                Statement on Form N-1A of Columbia Funds Trust II (File Nos.
                2-66976 and 811-3009), filed with the Commission on or about
                July 29, 2004.

    (10)(c)     Rule 18f-3(d) Plan under the Investment Company Act of 1940
                effective April 22, 1996, and amended and restated on December
                12, 2001, July 26, 2002, November 1, 2002, November 1, 2003 and
                February 17, 2004 - incorporated by reference to Exhibit (n) in
                Part C, Item 23(b) of Post-Effective Amendment No. 132 to the
                Registration Statement on Form N-1A of Columbia Funds Trust III
                (File Nos. 2-15184 and 811-881), filed with the Commission on or
                about February 25, 2004.

    (11)(a)     Form of opinion of Ropes & Gray LLP - incorporated by reference
                to Exhibit 11(a) to Part C, Item 16 of the Registrant's
                Registration Statement on Form N-14 (File No. 333-125739), as
                filed with the Commission on June 10, 2005 (Accession No.
                0000950135-05-003247).

    (11)(b)     Consent of Ropes & Gray LLP - incorporated by reference to
                Exhibit 11(b) to Part C, Item 16 of the Registrant's
                Registration Statement on Form N-14 (File No. 333-125739), as
                filed with the Commission on June 10, 2005 (Accession No.
                0000950135-05-003247).

    (12)        Opinion of Ropes & Gray LLP as to tax matters - Filed herewith.

    (13)(a)     Amended and Restated Shareholders' Servicing and Transfer Agent
                Agreement dated November 1, 2003 - incorporated by reference to
                Exhibit (h)(1) in Part C, Item 23(b) of Post-Effective Amendment
                No. 132 to the Registration Statement on Form N-1A of Columbia
                Funds Trust III (File Nos. 2-15184 & 811-881), filed with the
                Commission on or about February 25, 2004.

    (13)(b)     Schedule A of Amended and Restated Shareholders' Servicing and
                Transfer Agent Agreement dated November 1, 2003 - incorporated
                by reference to Exhibit (h)(2) in Part C, Item 23(b) of
                Post-Effective Amendment No. 132 to the Registration Statement
                on Form N-1A of Columbia Funds Trust III (File Nos. 2-15184 and
                811-881), filed with the Commission on or about February 25,
                2004.

    (13)(c)     Appendix I to the Amended and Restated Accounting and
                Bookkeeping Agreement between the Registrant and Columbia
                Management Advisors, Inc. dated November 1, 2003 - incorporated
                by reference to Exhibit (h)(3) in Part C, Item 23 of
                Post-Effective Amendment No. 132 to the Registration Statement
                on Form N-1A of Columbia Funds Trust III (File Nos. 2-15184 and
                811-881), filed with the Commission on or about February 25,
                2004.

    (13)(d)     Pricing and Bookkeeping Agreement dated November 1, 2003 -
                incorporated by reference to Exhibit (h)(4) in Part C, Item
                23(b) of Post-Effective Amendment No. 132 to the Registration
                Statement on Form N-1A of Columbia Funds Trust III (File Nos.
                2-15184 and 811-881), filed with the Commission on or about
                February 25, 2004.

    (13)(e)     Schedule A of Pricing and Bookkeeping Agreement between the
                Registrant and Columbia Management Advisors, Inc. dated November
                1, 2003 - incorporated by reference to Exhibit (h)(5) in Part C,
                Item 23 of Post-Effective Amendment No. 132 to the Registration
                Statement on Form N-1A of Columbia Funds Trust III (File Nos.
                2-15184 and 811-881), filed with the Commission on or about
                February 25, 2004.

    (13)(f)     Appendix I of Pricing and Bookkeeping Agreement dated November
                1, 2003 - incorporated by reference to Exhibit (h)(6) in Part C,
                Item 23(b) of Post-Effective Amendment No. 132 to the
                Registration Statement on Form N-1A of Columbia Funds Trust III
                (File Nos. 2-15184 and 811-881), filed with the Commission on or
                about February 25, 2004.

    (13)(g)     Opinion and Consent of Counsel - Incorporated by reference to
                Post-Effective Amendment No. 58 filed with the Commission via
                EDGAR on February 18, 2000.



    (13)(h)     Credit Facility with State Street Bank and Trust Company dated
                July 23, 2004 - incorporated by reference to exhibit (h)(7) in
                Part C, Item 23 of Post-Effective Amendment No. 64 to the
                Registration Statement on Form N-1A of Columbia Funds Trust II
                (File Nos. 2-66976 and 811-3009), filed with the Commission on
                or about July 27, 2004.

    (14)        Consent of PricewaterhouseCoopers LLP, Independent Registered
                Public Accounting Firm - incorporated by reference to Exhibit 14
                to Part C, Item 16 of the Registrant's Registration Statement on
                Form N-14 (File No. 333-125739), as filed with the Commission on
                June 10, 2005 (Accession No. 0000950135-05-003247).

    (15)        Not Applicable.

    (16)        Power of Attorney for: Douglas A. Hacker, Janet Langford Kelly,
                Richard W. Lowry, William E. Mayer, Charles R. Nelson, John J.
                Neuhauser, Patrick J. Simpson, Thomas E. Stitzel, Thomas C.
                Theobald, Anne-Lee Verville and Richard L. Woolworth --
                incorporated by reference to Exhibit 16 to Part C, Item 16 of
                the Registrant's Registration Statement on Form N-14 (File No.
                333-125739), as filed with the Commission on June 10, 2005
                (Accession No. 0000950135-05-003247).

    (17)        Not Applicable

ITEM 17. UNDERTAKINGS

    (1) The undersigned Registrant agrees that prior to any public reoffering of
        the securities registered through the use of a prospectus which is a
        part of this registration statement by any person or party who is deemed
        to be an underwriter within the meaning of Rule 145(c) of the Securities
        Act [17 CFR 230.145c], the reoffering prospectus will contain the
        information called for by the applicable registration form for the
        reofferings by persons who may be deemed underwriters, in addition to
        the information called for by the other items of the applicable form.

    (2) The undersigned registrant agrees that every prospectus that is filed
        under paragraph (1) above will be filed as a part of an amendment to the
        registration statement and will not be used until the amendment is
        effective, and that, in determining any liability under the 1933 Act,
        each post-effective amendment shall be deemed to be a new registration
        statement for the securities offered herein, and the offering of the
        securities at that time shall be deemed to be the initial bona fide
        offering of them.


                                     NOTICE

A copy of the Agreement and Declaration of Trust, as amended, of Columbia Funds
Series Trust I (the "Trust") is on file with the Secretary of The Commonwealth
of Massachusetts and notice is hereby given that this instrument has been
executed on behalf of the Trust by an officer of the Trust as an officer and by
its Trustees as trustees and not individually, and the obligations of or arising
out of this instrument are not binding upon any of the Trustees, officers or
shareholders individually but are binding only upon the assets and property of
the Trust.





                                   SIGNATURES

         As required by the Securities Act of 1933, as amended, this
Registration Statement has been signed on behalf of the Registrant, in the City
of Boston and The Commonwealth of Massachusetts, on the 17th day of April, 2006.

                                           COLUMBIA FUNDS SERIES TRUST I

                                           By:      /s/  Christopher L. Wilson
                                                    ----------------------------
                                           Name:    Christopher L. Wilson
                                           Title:   President

         As required by the Securities Act of 1933, as amended, this
Registration Statement has been signed by the following persons in their
capacities and on the dates indicated.



               Signature                                          Title                                Date
               ---------                                          -----                                ----
                                                                                            
/s/  Christopher L. Wilson
- ---------------------------
Christopher L. Wilson                              President (Chief Executive Officer)             April 17, 2006

/s/ J. Kevin Connaughton
- ---------------------------
J. Kevin Connaughton                               Treasurer (Principal Financial Officer)         April 17, 2006

/s/ Michael G. Clarke
- ---------------------------
Michael G. Clarke                                  Chief Accounting Officer (Principal             April 17, 2006
                                                   Accounting Officer)

/s/ Douglas A. Hacker*
- ---------------------------
Douglas A. Hacker                                  Trustee                                         April 17, 2006

/s/ Janet Langford Kelly*
- ---------------------------
Janet Langford Kelly                               Trustee                                         April 17, 2006

/s/ Richard W. Lowry*
- ---------------------------
Richard W. Lowry                                   Trustee                                         April 17, 2006

/s/ William E. Mayer*
- ---------------------------
William E. Mayer                                   Trustee                                         April 17, 2006

/s/ Charles R. Nelson*
- ---------------------------
Charles R. Nelson                                  Trustee                                         April 17, 2006

/s/ John J. Neuhauser*
- ---------------------------
John J. Neuhauser                                  Trustee                                         April 17, 2006

/s/ Patrick J. Simpson*
- ---------------------------
Patrick J. Simpson                                 Trustee                                         April 17, 2006

/s/ Thomas E. Stitzel*
- ---------------------------
Thomas E. Stitzel                                  Trustee                                         April 17, 2006

/s/ Thomas C. Theobald*
- ---------------------------
Thomas C. Theobald                                 Trustee                                         April 17, 2006

/s/ Anne-Lee Verville*
- ---------------------------
Anne-Lee Verville                                  Trustee                                         April 17, 2006






                                                                                            
/s/ Richard L. Woolworth*
- ---------------------------
Richard L. Woolworth                               Trustee                                         April 17, 2006




                                                 *By:  /s/ J. Kevin Connaughton,
                                                       -------------------------
                                                         Attorney-in-Fact
                                                         April 17, 2006




                                  EXHIBIT INDEX

(12)     Opinion of Ropes & Gray LLP as to tax matters