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SCHEDULE 13G
 (12/31/97)

MEDFORD BANCORP INC
Cusip # 584131106
Amendment

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Cusip # 584131106

Item  1:    REPORTING PERSONS
            Dimensional Fund Advisors Inc. (Tax ID: 22-2370029)

Item  4:    CITIZENSHIP
            Delaware Corporation

Item  5:    SOLE VOTING POWER
            243,200   (See Note 1)*
              * Persons who are officers of Dimensional Fund Advisors
              Inc. also serve as officers of DFA Investment Dimensions
              Group Inc., (the "Fund") and The DFA Investment Trust
              Company (the "Trust"), each an open-end management
              investment company registered under the Investment
              Company Act of 1940.  In their capacities as officers of
              the Fund and the Trust, these persons vote 38,200
              additional shares which are owned by the Fund and
              54,100    shares which are owned by the Trust. (Included
              in Item 7 of this page of this Schedule)

Item  6:    SHARED VOTING POWER --
            None

Item  7:    SOLE DISPOSITIVE POWER --
            335,500   (See Note 1)

Item  8:    SHARED DISPOSITIVE POWER --
            0

Item  9:    AGGREGATE AMOUNT BENEFICIALLY OWNED --
            335,500   (See Note 1)

Item 11:    PERCENT OF CLASS REPRESENTED BY LINE 9 --
            7.39  (See Note 1)

Item 12:    TYPE OF REPORTING PERSON --
            IA

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ITEM 1(A).  NAME OF ISSUER

            MEDFORD BANCORP INC

ITEM 1(B).  ADDRESS OF ISSUER

            29 High Street
            Medford, MA 02155


ITEM 2(A).  NAME OF PERSON FILING

            Dimensional Fund Advisors

ITEM 2(B).  ADDRESS OF PRINCIPAL BUSINESS OFFICE

            1299 Ocean Avenue, 11th Floor, Santa Monica, CA  90401

ITEM 2(C).  CITIZENSHIP

            A Delaware Corporation

ITEM 2(D).  TITLE OF CLASS OF SECURITIES

            Common Stock

ITEM 2(E).  CUSIP NUMBER

            584131106

ITEM 3.     This statement is filed pursuant to Rule 13d-1 (b), or
            13d-2 (b) and the person filing is an investment advisor
            registered under section 203 of the Investment Advisors
            Act of 1940.

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ITEM 4.     OWNERSHIP
ITEM 4(a).  AMOUNT BENEFICIALLY OWNED
            See Page 2, Item No. 9
ITEM 4(b).  PERCENT OF CLASS
            See Page 2, Item No. 11
ITEM 4(c).  NUMBER OF SHARE AS TO WHICH SUCH PERSON HAS:
      (i).  SOLE POWER TO VOTE OR DIRECT THE VOTE --
            See Page 2, Item No. 5
     (ii).  SHARED POWER TO VOTE OR TO DIRECT THE VOTE --
            None
    (iii).  SOLE POWER TO DISPOSE OR TO DIRECT DISPOSITION OF --
            See Page 2, Item No. 9
     (iv).  SHARE POWER TO DISPOSE OR TO DIRECT DISPOSISTION OF --
            None

ITEM 5.     OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS
            If this statement is being filed to report the fact that
            as of 12/31/97 the reporting person has ceased to be the
            beneficial owner of more than five percent of the class
            of securities, check the following: [ ]

ITEM 6.     OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF
            ANOTHER PERSON
            All Securities reported in this schedule are onwed by
            advisory clients of Dimensional Fund Advisors Inc., no one
            of which to the knowledge of Dimensional Fund Advisors Inc.
            owns more than 5% of the class.  Dimensional Fund Advisors
            Inc disclaims beneficial ownership of all such securities.

ITEM 7.     IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH
            ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING
            COMPANY:
            Not Applicable

ITEM 8.     IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP
            Not Applicable

ITEM 9.     NOTICE OF DISSOLUTION OF GROUP
            Not Applicable

ITEM 10.    CERTIFICATION
            By signing below I certify that, to the best of my knowledge
            and belief, the securities referred to above were acquired
            in the ordinary course of business and were not acquired for
            the purpose of and do not have the effect of changing or
            influencing the control of the issuer of such securities
            and were not acquired in connection with or as a participant
            in any transaction having such purposes or effect.

(Note 1): All securities reported on the schedule are owned by advisory
          clients of Dimensional Fund Advisors Inc.  Dimensional Fund
          Advisors Inc. disclaims beneficial ownership of all such
          securities.

After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true,
complete are correct.

Signature

   Monday, February 6, 1998
Date

   Michael T. Scardina
   Vice President and Chief Finacial Officer
Name/Title