Report of Independent Registered Public Accounting Firm

To the Shareholders and Board of Trustees of
Pioneer Series Trust X:

In planning and performing our audit of the financial statements of Pioneer
Dynamic Credit Fund, Pioneer Fundamental Growth Fund and Pioneer Multi-Asset
Ultrashort Income Fund (the "Funds") (three funds constituting Pioneer Series
Trust X) as of and for the year ended March 31, 2020, in accordance with the
standards of the Public Company Accounting Oversight Board (United States),
we considered the Funds' 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
Funds' internal control over financial reporting.  Accordingly, we express no
such opinion.

The management of the Funds 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
U.S. 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 U.S. 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 Funds' 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 Funds' 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
March 31, 2020.

This report is intended solely for the information and use of management and
the Board of Trustees of Pioneer Series Trust X, 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
May 29, 2020