Exhibit (b)

                         NATIXIS CASH MANAGEMENT TRUST
                           SECTION 906 CERTIFICATION

   In connection with the report on Form N-CSR for the period ended
December 31, 2007 for the Registrant (the "Report"), the undersigned each
hereby certifies to the best of his knowledge, pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that:

   1. the Report complies with the requirements of Section 13(a) or 15(d) of
the Securities and Exchange Act of 1934, as applicable; and

   2. the information contained in the Report fairly presents, in all material
respects, the financial condition and results of operations of the Registrant.

Natixis Cash Management Trust           Natixis Cash Management Trust

By:   /s/ John T. Hailer                By:   /s/ Michael C. Kardok
      --------------------------------        ---------------------------------
      John T. Hailer                          Michael C. Kardok
      President and Chief Executive           Treasurer
      Officer

Date: February 21, 2008                 Date: February 21, 2008

A signed original of this written statement required by Section 906, or other
document authenticating, acknowledging, or otherwise adopting the signature
that appears in typed form within the electronic version of this written
statement required by Section 906, has been provided to the Natixis Cash
Management Trust, and will be retained by the Natixis Cash Management Trust and
furnished to the Securities and Exchange Commission or its staff upon request.