UNDERWRITING AGREEMENT

   THIS UNDERWRITING AGREEMENT, dated this 3rd day of July, 2017, by and
between Pioneer Asset Allocation Trust, a Delaware statutory trust ("Trust"),
on behalf of its series Pioneer Solutions - Balanced Fund, Pioneer Solutions -
Conservative Fund and Pioneer Solutions - Growth Fund and Amundi Pioneer
Distributor, Inc., a Massachusetts corporation (the "Underwriter").

                                  WITNESSETH

   WHEREAS, the Trust is registered as an open-end management investment
company under the Investment Company Act of 1940, as amended (the "1940 Act"),
and has filed a registration statement (the "Registration Statement") with the
Securities and Exchange Commission (the "Commission") for the purpose of
registering shares of beneficial interest for public offering under the
Securities Act of 1933, as amended;

   WHEREAS, the Underwriter engages in the purchase and sale of securities both
as a broker and a dealer and is registered as a broker-dealer with the
Commission and is a member in good standing of the Financial Industry
Regulatory Authority ("FINRA");

   WHEREAS, the parties hereto deem it mutually advantageous that the
Underwriter should act as Principal Underwriter, as defined in the 1940 Act,
for the sale to the public of the shares of beneficial interest of the
securities portfolio of each series of the Trust which the Trustees may
establish from time to time (individually, a "Portfolio" and collectively, the
"Portfolios"); and

   NOW, THEREFORE, in consideration of the mutual covenants and benefits set
forth herein, the Trust and the Underwriter do hereby agree as follows:

   1. The Trust hereby grants to the Underwriter the right and option to
purchase shares of beneficial interest of each class of each Portfolio of the
Trust (the "Shares") for sale to investors either directly or indirectly
through other broker-dealers. The Underwriter is not required to purchase any
specified number of Shares, but will purchase from the Trust only a sufficient
number of Shares as may be necessary to fill unconditional orders received from
time to time by the Underwriter from investors and dealers.

   2. The Underwriter shall offer Shares to the public at an offering price
based upon the net asset value of the Shares, to be calculated for each class
of Shares as described in the Registration Statement, including the
Prospectus(es), filed with the Commission and in effect at the time of the
offering, plus sales charges as approved by the Underwriter and the Trustees of
the Trust and as further outlined in the Trust's Prospectus(es). The offering
price shall be subject to any provisions set forth in the Prospectus(es) from
time to time with respect thereto, including, without limitation, rights of
accumulation, letters of intention, exchangeability of Shares,



reinstatement privileges, net asset value purchases by certain persons and
reinvestments of dividends and capital gain distributions.

   3. In the case of all Shares sold to investors through other broker-dealers,
a portion of applicable sales charges will be reallowed to such broker-dealers
who are members of FINRA or, in the case of certain sales by banks or certain
sales to foreign nationals, to brokers or dealers exempt from registration with
the Commission. The concession reallowed to broker-dealers shall be set forth
in a written sales agreement and shall be generally the same for broker-dealers
providing comparable levels of sales and service.

   4. This Agreement shall terminate on any anniversary hereof if its terms and
renewal have not been approved by a majority vote of the Trustees of the Trust
voting in person, including a majority of its Trustees who are not "interested
persons" of the Trust and who have no direct or indirect financial interest in
the operation of the Underwriting Agreement (the "Qualified Trustees"), at a
meeting of Trustees called for the purpose of voting on such approval. This
Agreement may also be terminated at any time, without payment of any penalty,
by the Trust on 60 days' written notice to the Underwriter, or by the
Underwriter upon similar notice to the Trust. This Agreement may also be
terminated by a party upon five (5) days' written notice to the other party in
the event that the Commission has issued an order or obtained an injunction or
other court order suspending effectiveness of the Registration Statement
covering the Shares. Finally, this Agreement may also be terminated by the
Trust upon five (5) days' written notice to the Underwriter provided either of
the following events has occurred: (i) FINRA has expelled the Underwriter or
suspended its membership in that organization; or (ii) the qualification,
registration, license or right of the Underwriter to sell Shares in a
particular state has been suspended or cancelled in a state in which sales of
Shares during the most recent 12-month period exceeded 10% of all Shares sold
by the Underwriter during such period.

   5. The compensation for the services of the Underwriter as a principal
underwriter under this Agreement shall be:

   With respect to Class A Shares (i) that part of the sales charge which is
   retained by the Underwriter after allowance of discounts to dealers as set
   forth, if required, in the Registration Statement, including the Prospectus,
   filed with the Commission and in effect at the time of the offering, as
   amended, and (ii) those amounts payable to the Underwriter as reimbursement
   of expenses pursuant to any distribution plan for the Trust which may be in
   effect.

   With respect to Class C Shares (i) that part of the front-end sales charge
   which is retained by the Underwriter after allowance of discounts to dealers
   as set forth, if required, in the Registration Statement, including the
   Prospectus, filed with the Commission and in effect at the time of the
   offering, as amended, (ii) the Distribution Fee, if any, payable from time
   to time to the Underwriter under the Trust's Class C Distribution Plan and
   (iii) the contingent deferred sales charge payable with respect to Class C
   Shares sold through the Underwriter as set forth in the Registration
   Statement,

                                      2



   including the Prospectus, filed with the Commission and in effect at the
   time of the sale of such Class C Shares.

   With respect to Class R Shares (i) the Distribution Fee, if any, payable
   from time to time to the Underwriter under the Trust's Class R Distribution
   Plan and (ii) the sales charge payable, if any, with respect to Class R
   Shares sold through the Underwriter as set forth in the Registration
   Statement, including the Prospectus, filed with the Commission and in effect
   at the time of the sale of such Class R Shares.

   With respect to Class K Shares and Class Y Shares, the Underwriter shall not
   be entitled to any compensation.

   With respect to any future class of Shares, the Underwriter shall be
   entitled to such consideration as the Trust and the Underwriter shall agree
   at the time such class of Shares is established.

   6. Nothing contained herein shall relieve the Trust of any obligation under
its management contract or any other contract with any affiliate of the
Underwriter.

   7. The parties to this Agreement acknowledge and agree that all liabilities
arising hereunder, whether direct or indirect, of any nature whatsoever,
including without limitation, liabilities arising in connection with any
agreement of the Trust or its Trustees as set forth herein to indemnify any
party to this Agreement or any other person, if any, shall be satisfied out of
the assets of the Trust and that no Trustee, officer or holder of Shares shall
be personally liable for any of the foregoing liabilities. The Trust's
Agreement and Declaration of Trust describes in detail the respective
responsibilities and limitations on liability of the Trustees, officers and
holders of Shares.

   8. This Agreement shall automatically terminate in the event of its
assignment (as that term is defined in the 1940 Act).

   9. In the event of any dispute between the parties, this Agreement shall be
construed according to the laws of The Commonwealth of Massachusetts.

                                      3



   IN WITNESS WHEREOF, the parties hereto have caused this instrument to be
executed by their duly authorized officers and their seals to be hereto affixed
as of the day and year first above written.

ATTEST:                             PIONEER ASSET ALLOCATION TRUST
                                    On behalf of its series,
                                    Pioneer Solutions - Balanced Fund,
                                    Pioneer Solutions - Conservative Fund, and
                                    Pioneer Solutions - Growth Fund

/s/ Christopher J. Kelley                      By:   /s/ Lisa M. Jones
---------------------------                          --------------------------
Christopher J. Kelley                                Lisa M. Jones
Secretary                                            President

ATTEST:                                        AMUNDI PIONEER DISTRIBUTOR, INC.

/s/ Margaret C. Begley                         By:   /s/ Gregg M. Dooling
---------------------------                          --------------------------
Margaret C. Begley                                   Gregg M. Dooling
Secretary                                            Chief Financial Officer

                                      4