CERTIFICATIONS
--------------
I, John F. Cogan, Jr., certify that:

1. I have reviewed this report on Form N-Q of Pioneer Mid Cap Value Fund:

2. Based on my knowledge, this report does not contain any untrue
statement of a material fact or omit to state a material fact necessary to
make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by
this report;
3. Based on my knowledge, the schedule of investments included in this
report fairly presents in all material respects the investments of the
registrant as of the end of the fiscal quarter for which the report is filed;
4. The registrant's other certifying officer and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined
in Rule 30a-3(c) under the Investment Company Act of 1940) and internal
control over financial reporting ( as defined in Rule 30a-3(d) under the
Investment Company Act of 1940) for the registrant and have:
   a) designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our supervision, to
ensure that material information relating to the registrant, including its
consolidated subsidiaries, is made known to us by others within those
entities, particularly during the period in which this report is being
prepared;
   b) designed such internal control over financial reporting, or caused such
internal control over financial reporting to be designed under our
supervision, 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;
c) evaluated the effectiveness of the registrant's disclosure controls and
procedures and presented in this report our conclusions about the
effectiveness of the disclosure controls and procedures, as of a date within
90 days prior to the filing date of this report, based on such evaluation; and
   d) disclosed in this report any change in the registrant's internal control
over financial reporting that occurred during the registrant's most recent
fiscal quarter that has materially affected, or is reasonably likely to
materially affect, the registrant's internal control over financial reporting;
and
5. The registrant's other certifying officer and I have disclosed to the
registrant's auditors and the audit committee of the registrant's board of
directors (or persons performing the equivalent functions):
   a) all significant deficiencies and material weaknesses in the design or
operation of internal control over financial reporting which are reasonably
likely to adversely affect the registrant's ability to record, process,
summarize, and report financial information; and
b) any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrant's internal control
over financial reporting.


Date:  September 29, 2008 	                  /s/ John F. Cogan, Jr.
                                                  John F. Cogan, Jr.
                                                  President










CERTIFICATIONS
--------------
I, Mark Bradley, certify that:

1. I have reviewed this report on Form N-Q of Pioneer Mid Cap Value Fund:
2. Based on my knowledge, this report does not contain any untrue
statement of a material fact or omit to state a material fact necessary to
make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by
this report;
3. Based on my knowledge, the schedule of investments included in this
report fairly presents in all material respects the investments of the
registrant as of the end of the fiscal quarter for which the report is filed;
4. The registrant's other certifying officer and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined
in Rule 30a-3(c) under the Investment Company Act of 1940) and internal
control over financial reporting ( as defined in Rule 30a-3(d) under the
Investment Company Act of 1940) for the registrant and have:
   a) designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our supervision, to
ensure that material information relating to the registrant, including its
consolidated subsidiaries, is made known to us by others within those
entities, particularly during the period in which this report is being
prepared;
   b) designed such internal control over financial reporting, or caused such
internal control over financial reporting to be designed under our
supervision, 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;
c) evaluated the effectiveness of the registrant's disclosure controls and
procedures and presented in this report our conclusions about the
effectiveness of the disclosure controls and procedures, as of a date within
90 days prior to the filing date of this report, based on such evaluation; and
   d) disclosed in this report any change in the registrant's internal control
over financial reporting that occurred during the registrant's most recent
fiscal quarter that has materially affected, or is reasonably likely to
materially affect, the registrant's internal control over financial reporting;
and
5. The registrant's other certifying officer and I have disclosed to the
registrant's auditors and the audit committee of the registrant's board of
directors (or persons performing the equivalent functions):
   a) all significant deficiencies and material weaknesses in the design or
operation of internal control over financial reporting which are reasonably
likely to adversely affect the registrant's ability to record, process,
summarize, and report financial information; and
b) any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrant's internal control
over financial reporting.



Date:  September 29, 2008    	       		  /s/ Mark Bradley
                                                  Mark Bradley
                                                  Treasurer