As filed with the Securities and Exchange Commission on September 27, 2005

                                                             File No. 333-126370


                                  United States
                       Securities and Exchange Commission
                             Washington, D.C. 20549

                                    FORM N-14


             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                         Pre-Effective Amendment No. __
                         Post-Effective Amendment No. 2
                                                     ---

                        (Check appropriate box or boxes)


                    PIONEER IBBOTSON ASSET ALLOCATION SERIES

               (Exact Name of Registrant as Specified in Charter)


                                 (617) 742-7825
                        (Area Code and Telephone Number)

                  60 State Street, Boston, Massachusetts 02109
(Address of Principal Executive Offices: Number, Street, City, State, Zip Code)

                            Dorothy E. Bourassa, Esq.
                       Pioneer Investment Management, Inc.
                                 60 State Street
                           Boston, Massachusetts 02109
                     (Name and Address of Agent for Service)

Copies to:  David C. Phelan, Esq.
            Wilmer Cutler Pickering Hale and Dorr LLP
            60 State Street
            Boston, Massachusetts 02109

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 Post-Effective Amendment No. 1 to the
Registrant's Registration Statement on Form N-14 (File No. 333-126370), as filed
with the Commission on August 22, 2005 (Accession No. 0001145443-05-001882).




                                     PART C

                                OTHER INFORMATION
                    PIONEER IBBOTSON ASSET ALLOCATION SERIES
    (On behalf of its series, Pioneer Ibbotson Aggressive Allocation Series,
                  Pioneer Ibbotson Growth Allocation Series and
                  Pioneer Ibbotson Moderate Allocation Series)

ITEM 15. INDEMNIFICATION

No change from the information set forth in Item 25 of the most recently filed
Registration Statement of Pioneer Ibbotson Asset Allocation Series (the
"Registrant") on Form N-1A under the Securities Act of 1933 and the Investment
Company Act of 1940 (File Nos. 333-114788 and 811-21569) as filed with the
Securities and Exchange Commission on September 20, 2005 (Accession No.
0001288255-05-000009), which information is incorporated herein by reference.

ITEM 16. EXHIBITS


                                                                           
(1)(a)         Agreement and Declaration of Trust                                (1)

(1)(b)         Amended and Restated Declaration of Trust                         (2)

(1)(c)         Amendment to Amended and Restated Agreement and
               Declaration of Trust                                              (5)

(2)            By-Laws                                                           (2)

(3)            Not applicable

(4)(a)         Agreement and Plan of Reorganization for Pioneer Ibbotson         (*)
               Moderate Allocation Fund

(4)(b)         Agreement and Plan of Reorganization for Pioneer Ibbotson         (*)
               Aggressive Allocation Fund and Pioneer Ibbotson Growth
               Allocation Fund

(5)            Reference is made to Exhibits (1) and (2) hereof

(6)(a)         Management Contract                                               (2)

(6)(b)         Sub-Advisory Agreement between Pioneer Investment                 (5)
               Management, Inc. and Ibbotson Associates Advisors, LLC
               ("Ibbotson")

(6)(c)         Amendment to Sub-Advisory Agreement between Pioneer               (7)
               Investment Management, Inc. and Ibbotson




                                                                           
(6)(d)         Amended and Restated Expense Limitation Agreement                 (6)

(7)(a)         Underwriting Agreement with Pioneer Funds Distributor, Inc.       (2)

(7)(b)         Dealer Sales Agreement                                            (9)

(8)            Not applicable

(9)            Custodian Agreement with Brown Brothers Harriman & Co.            (2)
               ("BBH")

(10)(a)        Multiple Class Plan Pursuant to Rule 18f-3 for Pioneer Ibbotson   (2)
               Moderate Allocation Fund

(10)(b)        Multiple Class Plan Pursuant to Rule 18f-3 for Pioneer Ibbotson   (2)
               Growth Allocation Fund

(10)(c)        Multiple Class Plan Pursuant to Rule 18f-3 for Pioneer Ibbotson   (2)
               Aggressive Allocation Fund

(10)(d)        Class A Shares Distribution Plan for Pioneer Ibbotson Moderate    (2)
               Allocation Fund

(10)(e)        Class A Shares Distribution Plan for Pioneer Ibbotson Growth      (2)
               Allocation Fund

(10)(f)        Class A Shares Distribution Plan for Pioneer Ibbotson             (2)
               Aggressive Allocation Fund

(10)(g)        Class B Shares Distribution Plan for Pioneer Ibbotson Moderate    (2)
               Allocation Fund

(10)(h)        Class B Shares Distribution Plan for Pioneer Ibbotson Growth      (2)
               Allocation Fun

(10)(i)        Class B Shares Distribution Plan for Pioneer Ibbotson             (2)
               Aggressive Allocation Fund

(10)(j)        Class C Shares Distribution Plan for Pioneer Ibbotson Moderate    (2)
               Allocation Fund

(10)(k)        Class C Shares Distribution Plan for Pioneer Ibbotson Growth      (2)
               Allocation Fund

(10)(l)        Class C Shares Distribution Plan for Pioneer Ibbotson             (2)
               Aggressive Allocation Fund

(11)           Opinion of Counsel (legality of securities being offered)         (6)

(12)           Opinions as to Tax Matters                                        (*)

(13)(a)        Investment Company Service Agreement between the Registrant       (2)
               and Pioneer Investment Shareholder Services, Inc.

(13)(b)        Administration Agreement between the Registrant and Pioneer       (3)
               Investment Management, Inc. (formerly, Pioneering Services
               Corporation)

(13)(c)        Administrative and Fund Accounting Agency Agreement               (7)
               between the Registrant and BBH




                                                                           
(13)(d)        Asset Allocation Administrative Agreement between the             (7)
               Registrant and BBH

(13)(e)        Services Agreement for Class Y Shares                             (*)

(14)           Consent of Independent Registered Public Accounting Firm          (9)

(15)           Not applicable

(16)           Powers of Attorney                                                (7)

(17)(a)        Code of Ethics - Pioneer                                          (5)

(17)(b)        Code of Ethics - Ibbotson                                         (5)

(17)(b)        Form of Proxy Card                                                (6)



(1) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Initial Registration Statement on Form N-1A (File Nos.
333-114788 and 811-21569), as filed with the Securities and Exchange Commission
on April 23, 2004 (Accession no. 0001288255-04-000006).

(2) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Pre-effective Amendment No. 2 to the Registration
Statement on Form N-1A (File Nos. 333-114788 and 811-21569), as filed with the
Securities and Exchange Commission on August 6, 2004 (Accession no.
0001016964-04-000333).

(3) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Post-effective Amendment No. 1 to the Registration
Statement on Form N-1A (File Nos. 333-114788 and 811-21569), as filed with the
Securities and Exchange Commission on August 9, 2004 (Accession no.
0001016964-04-000353).

(4) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Post-effective Amendment No. 2 to the Registration
Statement on Form N-1A (File Nos. 333-114788 and 811-21569), as filed with the
Securities and Exchange Commission on February 28, 2005 (Accession no.
0001016964-05-000055).

(5) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Post-effective Amendment No. 3 to the Registration
Statement on Form N-1A (File Nos. 333-114788 and 811-21569), as filed with the
Securities and Exchange Commission on May 6, 2005 (Accession no.
0001016964-05-000218).

(6) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Registration Statement on Form N-14 (File No. 333-126370),
as filed with




the Securities and Exchange Commission on July 5, 2005 (Accession no.
0001145443-05-001510).

(7) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Post-effective Amendment No. 4 to the Registration
Statement on Form N-1A (File Nos. 333-114788 and 811-21569), as filed with the
Securities and Exchange Commission on July 15, 2005 (Accession no.
0001288255-05-000003).

(8) Previously filed. Incorporated herein by reference from the exhibits filed
with Pre-Effective Amendment No. 1 to the Registrant's Registration Statement on
Form N-14 (File No. 333-126370), as filed with the Securities and Exchange
Commission on August 19, 2005 (Accession no. 0001145443-05-001811).

(9) Previously filed. Incorporated herein by reference from the exhibits filed
with the Registrant's Post-effective Amendment No. 5 to the Registration
Statement on Form N-1A (File Nos. 333-114788 and 811-21569), as filed with the
Securities and Exchange Commission on September 20, 2005 (Accession no.
0001288255-05-000009).

(*)  Filed herewith.

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 part of
this Registration Statement by any person or party which is deemed to be an
underwriter within the meaning of Rule 145(c) of the Securities Act of 1933, 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 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 Securities Act of 1933, each
post-effective amendment shall be deemed to be a new registration statement for
the securities offered therein, and the offering of the securities at that time
shall be deemed to be the initial bona fide offering of them.

(3)      The undersigned Registrant agrees that it shall file a final executed
version of the legal and consent opinion as to tax matters as an exhibit to the
subsequent post-effective amendment to its registration statement on Form N-14
filed with the SEC upon the consummation of the reorganization contemplated by
this Registration Statement on Form N-14.

(4)      Insofar as indemnification for liability arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Registrant pursuant




to the foregoing provisions, or otherwise the Registrant has been advised that
in the opinion of the Securities and Exchange Commission such indemnification is
against public policy as expressed in the Act and is, therefore, unenforceable.
In the event that a claim for indemnification against such liabilities (other
than the payment by the Registrant of expenses incurred or paid by a director,
officer or controlling person of the Registrant in the successful defense of any
action, suit or proceeding) is asserted by such director, officer or controlling
person in connection with the securities being registered, the Registrant will,
unless in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the Act and
will be governed by the final adjudication of such issue.




                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement on Form N-14 has been signed on behalf of the
Registrant, in the City of Boston and the Commonwealth of Massachusetts, on the
27th day of September, 2005.

                                       Pioneer Ibbotson Asset Allocation Series

                                       /s/ Osbert M. Hood
                                       -----------------------------------------
                                       Osbert M. Hood
                                       Executive Vice President

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the dates indicated.



             Signature                          Title                                Date
                                                                          
         *
- ---------------------------           Chairman of the Board, Trustee,
John F. Cogan, Jr.                    and President

         *
- ---------------------------           Chief Financial Officer,
Vincent Nave                          Principal Accounting Officer, and
                                      Treasurer
         *
- ---------------------------
Mary K. Bush                          Trustee

         *
- ---------------------------
David R. Bock                         Trustee

         *
- ---------------------------
Margaret B.W. Graham                  Trustee

         *
- ---------------------------
Marguerite A. Piret                   Trustee

         *
- ---------------------------
John Winthrop                         Trustee

*  By:   /s/ Osbert M. Hood                                                     September 27, 2005
         ------------------------------
         Osbert M. Hood, Attorney-in-Fact



                                  EXHIBIT INDEX

The following exhibits are filed as part of this Registration Statement:

Exhibit No.   Description


(4)(a)        Agreement and Plan of Reorganization for Pioneer Ibbotson Moderate
              Allocation Fund

(4)(b)        Agreement and Plan of Reorganization for Pioneer Ibbotson
              Aggressive Allocation Fund and Pioneer Ibbotson Growth Allocation
              Fund

(12)          Opinions as to Tax Matters

(13)(e)       Services Agreement for Class Y Shares