Multiple Class Plan

 PIONEER FUND

                   Multiple Class Plan Pursuant to Rule 18f-3
 Class A Shares, Class B Shares, Class C Shares, Class R Shares, Class Y Shares
                            and Investor Class Shares

                                  May 1, 2005

         Each class of shares of Pioneer Fund (the  "Fund")  will have the same
relative  rights and privileges  and be subject to the same sales charges,  fees
and expenses,  except as set forth below. The Board of Trustees may determine in
the  future  that  other  distribution arrangements,  allocations  of  expenses
(whether  ordinary or  extraordinary) or services to be provided to a class of
shares are  appropriate and amend this Multiple Class Plan  accordingly  without
the  approval of shareholders of any class.  Except as set forth in the Fund's
prospectus(es),  shares  may be exchanged only for shares of the same class of
another Pioneer mutual fund.

         Article I.  Class A Shares

         Class A Shares are sold at net asset value per share and subject to the
initial sales charge schedule or contingent deferred sales charge ("CDSC") and
minimum purchase requirements as set forth in the Fund's prospectus. Class A
Shares shall be entitled to the shareholder services set forth from time to time
in the Fund's prospectus with respect to Class A Shares. Class A Shares are
subject to fees calculated as a stated percentage of the net assets attributable
to Class A Shares under the Fund's Class A Rule 12b-1 Distribution Plan as set
forth in such Distribution Plan. The Class A Shareholders have exclusive voting
rights, if any, with respect to the Fund's Class A Rule 12b-1 Distribution Plan.
Transfer agency fees are allocated to Class A Shares on a per account basis
except to the extent, if any, such an allocation would cause the Fund to fail to
satisfy any requirement necessary to obtain or rely on a private letter ruling
from the Internal Revenue Service ("IRS") relating to the issuance of multiple
classes of shares. Class A Shares shall bear the costs and expenses associated
with conducting a shareholder meeting for matters relating to Class A Shares.

         The initial purchase date for Class A Shares acquired through (i)
reinvestment of dividends on Class A Shares or (ii) exchange from another
Pioneer mutual fund will be deemed to be the date on which the original Class A
Shares were purchased.

         Article II.  Class B Shares

         Class B Shares are sold at net asset value per share without the
imposition of an initial sales charge. However, Class B Shares redeemed within a
specified number of years of purchase will be subject to a CDSC as set forth in
the Fund's prospectus. Class B Shares are sold subject to the minimum purchase
requirements set forth in the Fund's prospectus. Class B Shares shall be
entitled to the shareholder services set forth from time to time in the Fund's
prospectus with respect to Class B Shares. Class B Shares are subject to fees
calculated as a stated percentage of the net assets attributable to Class B
Shares under the Class B Rule 12b-1 Distribution Plan as set forth in such
Distribution Plan. The Class B Shareholders of the Fund have exclusive voting
rights, if any, with respect to the Fund's Class B Rule 12b-1 Distribution Plan.
Transfer agency fees are allocated to Class B Shares on a per account basis
except to the extent, if any, such an allocation would cause the Fund to fail to
satisfy any requirement necessary to obtain or rely on a private letter ruling
from the IRS relating to the issuance of multiple classes of shares. Class B
Shares shall bear the costs and expenses associated with conducting a
shareholder meeting for matters relating to Class B Shares.

         Class B Shares will automatically convert to Class A Shares of the Fund
at the end of a specified number of years after the initial purchase date of
Class B Shares, except as provided in the Fund's prospectus. Such conversion
will occur at the relative net asset value per share of each class without the
imposition of any sales charge, fee or other charge. The conversion of Class B
Shares to Class A Shares may be suspended if it is determined that the
conversion constitutes or is likely to constitute a taxable event under federal
income tax laws.

         The initial purchase date for Class B Shares acquired through (i)
reinvestment of dividends on Class B Shares or (ii) exchange from another
Pioneer mutual fund will be deemed to be the date on which the original Class B
Shares were purchased.

         Article III.  Class C Shares

         Class C Shares are sold at net asset value per share without the
imposition of an initial sales charge. Class C Shares redeemed within one (1)
year of purchase will be subject to a CDSC as set forth in the Fund's
prospectus. Class C Shares are sold subject to the minimum purchase requirements
set forth in the Fund's prospectus. Class C Shares shall be entitled to the
shareholder services set forth from time to time in the Fund's prospectus with
respect to Class C Shares. Class C Shares are subject to fees calculated as a
stated percentage of the net assets attributable to Class C Shares under the
Class C Rule 12b-1 Distribution Plan as set forth in such Distribution Plan. The
Class C Shareholders of the Fund have exclusive voting rights, if any, with
respect to the Fund's Class C Rule 12b-1 Distribution Plan. Transfer agency fees
are allocated to Class C Shares on a per account basis except to the extent, if
any, such an allocation would cause the Fund to fail to satisfy any requirement
necessary to obtain or rely on a private letter ruling from the IRS relating to
the issuance of multiple classes of shares. Class C Shares shall bear the costs
and expenses associated with conducting a shareholder meeting for matters
relating to Class C Shares.

         The initial purchase date for Class C Shares acquired through (i)
reinvestment of dividends on Class C Shares or (ii) exchange from another
Pioneer mutual fund will be deemed to be the date on which the original Class C
Shares were purchased.

         Article IV.  Class R Shares

         Class R Shares are sold at net asset value per share without an initial
sales charge or CDSC as set forth in the Fund's prospectus. Class R Shares are
sold to retirement plans that meet the eligibility requirements for Class R
Shares set forth in the Fund's prospectus. Class R Shares shall be entitled to
the shareholder services set forth from time to time in the Fund's prospectus
with respect to Class R Shares. Class R Shares are subject to fees calculated as
a stated percentage of the net assets attributable to Class R Shares under the
Class R Rule 12b-1 Distribution Plan as set forth in such Distribution Plan. The
Class R Shareholders of the Fund have exclusive voting rights, if any, with
respect to the Fund's Class R Rule 12b-1 Distribution Plan. Transfer agency fees
are allocated to Class R Shares on a per account basis except to the extent, if
any, such an allocation would cause the Fund to fail to satisfy any requirement
necessary to obtain or rely on a private letter ruling from the IRS relating to
the issuance of multiple classes of shares. Class R Shares shall bear the costs
and expenses associated with conducting a shareholder meeting for matters
relating to Class R Shares.

         The initial purchase date for Class R Shares acquired through (i)
reinvestment of dividends on Class R Shares or (ii) exchange from another
Pioneer mutual fund will be deemed to be the date on which the original Class R
Shares were purchased.

         Article V.  Class Y Shares

         Class Y Shares are sold at net asset value per share without the
imposition of an initial sales charge. Class Y Shares are not subject to a CDSC
upon redemption regardless of the length of the period of time such shares are
held. Class Y Shares are sold subject to the minimum purchase requirements set
forth in the Fund's prospectus. Class Y Shares shall be entitled to the
shareholder services set forth from time to time in the Fund's prospectus with
respect to Class Y Shares.

         Class Y Shares are not subject to fees payable under a distribution or
other plan adopted pursuant to Rule 12b-1 under the Investment Company Act of
1940, as amended (the "Act"). The Class Y Shareholders of the Fund have
exclusive voting rights, if any, with respect to the Fund's possible future
adoption of a Class Y Rule 12b-1 Distribution Plan. Transfer agency fees are
allocated to Class Y Shares on a per account basis except to the extent, if any,
such an allocation would cause the Fund to fail to satisfy any requirement
necessary to obtain or rely on a private letter ruling from the IRS relating to
the issuance of multiple classes of shares. Class Y Shares shall bear the costs
and expenses associated with conducting a shareholder meeting for matters
relating to Class Y Shares.

         The initial purchase date for Class Y Shares acquired through (i)
reinvestment of dividends on Class Y Shares or (ii) exchange from another
Pioneer mutual fund will be deemed to be the date on which the original Class Y
Shares were purchased.

         Article VI.  Investor Class

         Investor Class Shares are only issued in connection with
reorganizations of other investment companies, or series thereof, into the Fund
or upon reinvestment of dividends on Investor Class Shares. Investor Class
Shares shall be entitled to the shareholder services set forth from time to time
in the Fund's prospectus with respect to Investor Class Shares. Investor Class
Shares are not subject to a Rule 12b-1 Distribution Plan. Transfer agency fees
are allocated to Investor Class Shares on a per account basis except to the
extent, if any, such an allocation would cause the Fund to fail to satisfy any
requirement necessary to obtain or rely on a private letter ruling from the IRS
relating to the issuance of multiple classes of shares. Investor Class Shares
shall bear the costs and expenses associated with conducting a shareholder
meeting for matters relating to Investor Class Shares.

         Investor Class Shares will automatically convert to Class A Shares of
the Fund on the second anniversary of the closing of the issuance of such
Investor Class Shares. Such conversion will occur at the relative net asset
value per share of each class without the imposition of any sales charge, fee or
other charge. The conversion of Investor Class Shares to Class A Shares may be
suspended if it is determined that the conversion constitutes or is likely to
constitute a taxable event under federal income tax laws.

         The initial purchase date for Investor Class Shares acquired through
(i) reinvestment of dividends on Class Shares or (ii) exchange from another
Pioneer mutual fund will be deemed to be the date on which the original Investor
Class Shares were issued.

         Article VII.  Approval by Board of Trustees

         This Multiple Class Plan shall not take effect until it has been
approved by the vote of a majority (or whatever greater percentage may, from
time to time, be required under Rule 18f-3 under the Act) of (a) all of the
Trustees of the Fund and (b) those of the Trustees who are not "interested
persons" (as such term may be from time to time defined under the Act) of the
Fund.

         Article VIII.  Amendments

         No material amendment to this Multiple Class Plan shall be effective
unless it is approved by the Board of Trustees of the Fund in the same manner as
is provided for approval of this Multiple Class Plan in Article VII. 

Basic Info X:

Name: Multiple Class Plan
Type: Multiple Class Plan
Date: April 29, 2005
Company: PIONEER FUND /MA/
State: Delaware

Other info: