Report of Independent Registered Public
Accounting Firm


To the Shareowners and Board of Trustees of
Pioneer Money Market Trust

In planning and performing our audit of the financial
statements of the Pioneer Cash Reserves Fund, a
series of Pioneer Money Market Trust (the Company)
as of and for the year ended December 31, 2010, in
accordance with the standards of the Public Company
Accounting Oversight Board (United States), we
considered the Company's internal control over
financial reporting, including controls over safeguarding
securities, as a basis for designing our auditing
procedures for the purpose of expressing our opinion
on the financial statements and to comply with the
requirements of Form N-SAR, but not for the purpose
of expressing an opinion on the effectiveness of the
Company's internal control over financial reporting.
Accordingly, we express no such opinion.
The management of the Company is responsible for
establishing and maintaining effective internal control
over financial reporting. In fulfilling this responsibility,
estimates and judgments by management are required
to assess the expected benefits and related costs of
controls. A company's internal control over financial
reporting is a process designed to provide reasonable
assurance regarding the reliability of financial reporting
and the preparation of financial statements for external
purposes in accordance with generally accepted
accounting principles. A company's internal control
over financial reporting includes those policies and
procedures that (1) pertain to the maintenance of
records that, in reasonable detail, accurately and fairly
reflect the transactions and dispositions of the assets
of the company; (2) provide reasonable assurance that
transactions are recorded as necessary to permit
preparation of financial statements in accordance with
generally accepted accounting principles, and that
receipts and expenditures of the company are being
made only in accordance with authorizations of
management and directors of the company; and (3)
provide reasonable assurance regarding prevention or
timely detection of unauthorized acquisition, use or
disposition of a company's assets that could have a
material effect on the financial statements.
Because of its inherent limitations, internal control over
financial reporting may not prevent or detect
misstatements. Also, projections of any evaluation of
effectiveness to future periods are subject to the risk
that controls may become inadequate because of
changes in conditions, or that the degree of compliance
with the policies or procedures may deteriorate.
A deficiency in internal control over financial reporting
exists when the design or operation of a control does
not allow management or employees, in the normal
course of performing their assigned functions, to
prevent or detect misstatements on a timely basis. A
material weakness is a deficiency, or a combination of
deficiencies, in internal control over financial reporting,
such that there is a reasonable possibility that a
material misstatement of the company's annual or
interim financial statements will not be prevented or
detected on a timely basis.



Our consideration of the Company internal control over
financial reporting was for the limited purpose
described in the first paragraph and would not
necessarily disclose all deficiencies in internal control
that might be material weaknesses under standards
established by the Public Company Accounting
Oversight Board (United States). However, we noted
no deficiencies in the Company's internal control over
financial reporting and its operation, including controls
over safeguarding securities, that we consider to be a
material weakness as defined above as of December
31, 2010.
This report is intended solely for the information and
use of management and the Board of Trustees of
Pioneer Money Market Trust and the Securities and
Exchange Commission and is not intended to be and
should not be used by anyone other than these
specified parties.

Ernst & Young LLP


Boston, Massachusetts
February 25, 2011