BINGHAM McCUTCHEN LLP
                              ONE FEDERAL STREET
                          BOSTON, MASSACHUSETTS 02110

                                          January 27, 2014

VIA EDGAR
--- ------

Securities and Exchange Commission
Division of Investment Management
100 F Street, NE
Washington, D.C. 20549

Re:    Pioneer Series Trust XI (File Nos. 2-32773; 811-01835)
       Registration Statement on Form N-1A

Ladies and Gentlemen:

       This letter is to respond to comments we received from Mr. Derek Newman
of the Staff of the Division of Investment Management of the Securities and
Exchange Commission (the "Commission") regarding Post-Effective Amendment
No. 77 to the Registration Statement on Form N-1A of Pioneer Series Trust XI
(the "Registrant") relating to Pioneer Core Equity Fund. Following are the
Staff's comments and the Registrant's responses thereto:

I. General Comment

1.  Comment:   The Staff asked that the Registrant provide a letter to the
               Commission that includes certain "Tandy" acknowledgments with
               the Registrant's response to the Staff's comments.

    Response:  A Tandy representation letter executed in connection with the
               filing of this response is attached hereto as Exhibit A.

2.  Comment:   The Staff requested that the Registrant confirm that the
               disclosure in the Registration Statement reflects the
               reorganization of the Fund with Pioneer Research Fund as
               contemplated by the Registration Statement on Form N-14 filed
               by the Registrant on March 6, 2013.

    Response:  The Registrant confirms that the disclosure in the Registration
               Statement reflects the reorganization of the Fund with Pioneer
               Research Fund as contemplated by the Registration Statement on
               Form N-14 filed by the Registrant on March 6, 2013.

II. Comments Applicable to the Prospectus

A. Fees and Expenses

1.  Comment:   The Staff noted that the Registrant states that the Fund may
               invest in exchange-traded funds, and requested that the
               Registrant confirm that: (a) the Fund does not invest in
               exchange-traded funds or other investment companies to the
               extent that such investments represented 0.01% or more of the
               Fund's expenses and must be included in a separate acquired
               fund fees and expenses line item; and (b) any expenses related
               to investments in



               exchange-traded funds and other investment companies are
               reflected in the other expenses line item.

    Response:  The Registrant confirms that: (a) the Fund does not invest in
               exchange-traded funds or other investment companies to the
               extent that such investments represented 0.01% or more of the
               Fund's expenses and must be included in a separate acquired
               fund fees and expenses line item; and (b) any expenses related
               to investments in exchange-traded funds and other investment
               companies are reflected in the other expenses line item.

2.  Comment:   The Staff requested that the Registrant file the agreement
               relating to the expense limitation arrangement referenced in
               Footnote 1 to the Fee Table as an exhibit to the next
               Post-Effective Amendment to the Registrant's Registration
               Statement relating to the Fund.

    Response:  The Registrant confirms that it will file the agreement
               relating to the expense limitation arrangement referenced in
               Footnote 1 to the Fee Table as an exhibit to the next
               Post-Effective Amendment to the Registrant's Registration
               Statement relating to the Fund.

3.  Comment:   The Staff requested that the Registrant confirm that Class Y
               shares of the Fund are not subject to the expense limitation
               arrangement.

    Response:  The Registrant confirms that Class Y shares of the Fund are not
               subject to the expense limitation arrangement.

4.  Comment:   The Staff requested that the Registrant confirm that the
               expense limitation arrangement does not apply to acquired fund
               fees and expenses and, if so, revise Footnote 1 to the Fee
               Table accordingly.

    Response:  The Registrant confirms that the expense limitation arrangement
               does not apply to acquired fund fees and expenses and has
               revised Footnote 1 to the Fee Table accordingly.

5.  Comment:   The Staff noted that the Registrant states that the expense
               limitation arrangement may be terminated for a class only by
               agreement of the adviser and the Board of Trustees. The Staff
               requested that the Registrant confirm in its response that the
               Board of Trustees does not intend to terminate the arrangement
               during the next twelve months.

    Response:  The Registrant confirms that it has not been informed that the
               Board of Trustees intends to terminate the expense limitation
               arrangement during the next twelve months.

6.  Comment:   The Staff requested that the Registrant confirm in its response
               that the expense example reflects the expense limitation
               arrangement only in the calculation of the one year example,
               and only in year one of the calculations of the three year,
               five year and ten year examples.

    Response:  The Registrant confirms that the expense example reflects the
               expense limitation arrangement only in the calculation of the
               one year example, and only in year one of the calculations of
               the three year, five year and ten year examples.



B. Principal Risks of Investing in the Fund

1.  Comment:   The Staff suggested that the Registrant consider adding
               disclosure to the Derivatives Risk factor regarding the
               limitations on the Fund's ability to use certain instruments
               with which the Fund must comply in order to continue to claim
               an exclusion from registration as a "commodity pool operator"
               under the Commodity Exchange Act.

    Response:  The Registrant has added disclosure in the "More on the risks
               of investing in the fund" section of the prospectus to address
               the Staff's comment.

C. More on the Fund's Investment Objective and Strategies

1.  Comment:   The Staff noted that the Registrant states that "the fund may
               consider an ETF as an equity security for purposes of
               satisfying the fund's 80% policy if the ETF invests at least
               80% of its net assets in equity securities." The Staff
               requested that the Registrant explain in its response how
               counting such an investment toward the Fund's 80% policy is
               consistent with Staff guidance with respect to Rule 35d-1.

    Response:  The Registrant notes that the Staff indicated in the release
               adopting Rule 35d-1 that an investment company may include a
               synthetic instrument in its 80% basket if it has economic
               characteristics similar to the securities included in that
               basket. See Investment Company Act Release No. 24828 (Jan. 17,
               2001) at note 13. The Registrant believes that an ETF that
               invests at least 80% of its net assets in equity securities has
               economic characteristics similar to equity securities.
               Accordingly, the Registrant believes that counting such an
               investment toward the Fund's 80% policy is consistent with the
               Staff's guidance set forth in the Rule 35d-1 adopting release.

2.  Comment:   The Staff noted that the Registrant states that "non-U.S.
               issuers are issuers that are organized and have their principal
               offices outside of the United States." The Staff requested that
               Registrant confirm in its response that the disclosure is
               accurate, or whether the Registrant considers other factors in
               determining if a security is issued by a non-U.S. issuer, such
               as the currency in which the security is denominated or whether
               the issuer of the security derives at least 50% of its gross
               revenues or profits from goods or services produced in a
               non-U.S. country.

    Response:  The Registrant confirms that the disclosure referenced by the
               Staff is accurate.

   Please call the undersigned at (617) 951-8458 or Toby Serkin at
(617) 951-8760 with any questions.

                                                  Sincerely,

                                                  /s/ Jeremy Kantrowitz

                                                  Jeremy Kantrowitz

cc:    Terrence J. Cullen
       Christopher J. Kelley
       Roger P. Joseph
       Toby R. Serkin