Report of Independent Registered Public Accounting Firm

To the Shareholders and Board of Trustees of
Pioneer Mid Cap Value Fund:

In planning and performing our audit of the financial statements of Pioneer
Mid Cap Value Fund (the "Fund") as of and for the year ended October 31, 2018,
in accordance with the standards of the Public Company Accounting Oversight
Board (United States), we considered the Fund'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-CEN, but not for the purpose of expressing an opinion on the
effectiveness of the Fund's internal control over financial reporting.
Accordingly, we express no such opinion.

The management of the Fund 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 Fund's 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 Fund'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 October 31, 2018.

This report is intended solely for the information and use of management and
the Board of Trustees of Pioneer Mid Cap Value Fund, and the Securities and
Exchange Commission and is not intended to be and should not be used by
anyone other than these specified parties.


/s/ ERNST& YOUNG LLP

Boston, Massachusetts
December 21, 2018