Exhibit A

                            PIONEER SERIES TRUST XI
                                60 State 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:

   In connection with the review by the Staff of the Securities and Exchange
Commission (the "Commission") of Post-Effective Amendment No. 77 to the
Registration Statement on Form N-1A for Pioneer Series Trust XI relating to
Pioneer Core Equity Fund, filed on December 2, 2013, the Registrant
acknowledges that, with respect to filings made by the Registrant with the
Commission and reviewed by the Staff:

    (a)  the Registrant is responsible for the adequacy and accuracy of the
         disclosure in the filings;

    (b)  Staff comments or changes to disclosure in response to Staff comments
         in the filings reviewed by the Staff do not foreclose the Commission
         from taking any action with respect to the filings; and

    (c)  the Registrant may not assert Staff comments as a defense in any
         proceeding initiated by the Commission or any person under the federal
         securities laws of the United States.

                                             Sincerely,

                                             Pioneer Series Trust XI

                                             By:    /s/ Christopher J. Kelley
                                             Name:  Christopher J. Kelley
                                             Title: Secretary