
<PAGE>
 
                                                                    Exhibit 10.1

                 FIRST AMENDMENT TO REVOLVING CREDIT AGREEMENT
                 ---------------------------------------------


     This First Amendment to Revolving Credit Agreement is made and entered into
as of the ____ day of July, 1997, by and among BOSTON PROPERTIES LIMITED
PARTNERSHIP ("BPLP") and the Wholly-owned Subsidiaries which are listed on
Schedule 1 to a certain Revolving Credit Agreement dated as of June 23, 1997,
having their principal place at 8 Arlington Street, Boston, Massachusetts 02116,
BANKBOSTON, N.A. (formerly known as The First National Bank of Boston)
("BankBoston"), a national banking association, having its principal place of
business at 100 Federal Street, Boston, Massachusetts 02110, and the other
lending institutions which may become parties hereto pursuant to Section 20 of
the Revolving Credit Agreement and BANKBOSTON, N.A., as agent for itself and
each other Bank.

     The following sets forth the background to this First Amendment to
Revolving Credit Agreement:

     A.  The Borrower, BankBoston and the Agent entered into that certain
Revolving Credit dated as of June 23, 1997 (the "Credit Agreement"); and

     B.  The Borrower, BankBoston and the Agent wish to amend the Credit
Agreement as hereinafter provided.

     NOW, THEREFORE, in consideration of One Dollar ($1.00) and other good and
valuable consideration by each of the parties hereto to the other of them in
hand this day paid, the receipt and sufficiency of which are hereby
acknowledged, it is agreed as follows:

                                      -1-
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1.        Clauses (ii), (iii) and (iv) of the definition of Applicable Margin
     are deleted in their entirety and are replaced with the following:
   
          "(ii) For any period during which the Consolidated Total Indebtedness
          on the last day of a quarter is greater than 45% but less than or
          equal to 55% of the Consolidated Total Adjusted Asset Value for such
          quarter, the Applicable Margin will equal 1.1%.

          (iii) For any period during which the Consolidated Total Indebtedness
          on the last day of a quarter is greater than 35% but less than or
          equal to 45% of the Consolidated Total Adjusted Asset Value for such
          quarter, the Applicable Margin will equal 1%.

          (iv) For any period during which the Consolidated Total Indebtedness
          on the last day of a quarter is less than or equal to 35% of the
          Consolidated Total Adjusted Asset Value for such quarter, the
          Applicable Margin will equal .90%."

                                      -2-
<PAGE>
 
2.        The definition of Annualized Borrowing Base Properties Capital
     Expenditures is hereby deleted in its entirety and replaced with the
     following:

          "(i) with respect to any Real Estate Assets, which are Borrowing Base
          Properties, other than hotel properties, for any rolling four (4)
          calendar quarters, determined as of the last day of a calendar
          quarter, an amount equal to 25c multiplied by the total number of
                                          ---------- --
          square feet of the Real Estate Assets, which are Borrowing Base
          Properties, other than hotel properties on the last day of such
          calendar quarter; (ii) with respect to the Marriott Cambridge Center
          Hotel in Cambridge, Massachusetts for so long as it is a Borrowing
          Base Property, for any rolling four (4) calendar quarters, determined
          as of the last day of a calendar quarter, an amount equal to six
          percent (6%) of gross revenues as determined in accordance with GAAP
          for such four (4) calendar quarters; (iii) with respect to the
          Marriott Long Wharf Hotel in Boston, Massachusetts, for so long as it
          is a Borrowing Base Property, for any rolling four (4) calendar
          quarters, determined as of the last day of a calendar quarter, an
          amount equal to five percent (5%) of gross revenues as determined in
          accordance with GAAP for such four (4) calendar quarters and (iv) with
          respect to the hotel properties which are Borrowing Base Properties,
          other than the Marriott Long Wharf Hotel and the Marriott Cambridge
          Center Hotel, for any rolling four (4) calendar quarters, determined
          as of the last day of a calendar quarter, an amount equal to the
          applicable percentage of gross revenues as determined in accordance
          with GAAP for such four (4) calendar quarters, which is to be
          maintained on the books of Borrower or in a separate reserve account
          for the replacement or repair of such hotel's furniture, fixtures and
          equipment pursuant to the applicable hotel management agreement or
          franchise agreement (which such agreement shall be in form and
          substance customary for a national hotel franchise)."

                                      -3-
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3.        The definition of Annualized Capital Expenditures is hereby deleted in
     its entirety and replaced with the following:

          "(i) with respect to any Real Estate Assets other than hotel
          properties, for any rolling four (4) calendar quarters, determined as
          of the last day of a calendar quarter, an amount equal to 25c
          multiplied by the total number of square feet of the Real Estate
          ---------- --
          Assets other than hotel properties on the last day of such calendar
          quarter; (ii) with respect to the Marriott Cambridge Center Hotel in
          Cambridge, Massachusetts, for any rolling four (4) calendar quarters,
          determined as of the last day of a calendar quarter, an amount equal
          to six percent (6%) of gross revenues as determined in accordance with
          GAAP for such four (4) calendar quarters; (iii) with respect to the
          Marriott Long Wharf Hotel in Boston, Massachusetts, for any rolling
          four (4) calendar quarters, determined as of the last day of a
          calendar quarter, an amount equal to five percent (5%) of gross
          revenues as determined in accordance with GAAP for such four (4)
          calendar quarters and (iv) with respect to the hotel properties other
          than the Marriott Long Wharf Hotel and the Marriott Cambridge Center
          Hotel, for any rolling four (4) calendar quarters, determined as of
          the last day of a calendar quarter, an amount equal to the applicable
          percentage of gross revenues as determined in accordance with GAAP for
          such four (4) calendar quarters, which percentage shall be the
          percentage for each such hotel as is to be maintained on the books of
          the Borrower or in a separate reserve account for the replacement or
          repair of such hotel's furniture, fixtures and equipment pursuant to
          the applicable hotel management agreement or franchise agreement
          (which such agreement shall be in form and substance customary for a
          national hotel franchise)."

4.        The definition of Borrowing Base Value is hereby amended by deleting
     the word "Annual" contained in clause (ii) thereof and by replacing it with
     the following:

          "Annualized"

                                      -4-
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5.        The definition of Consolidated EBITDA is hereby amended by inserting
     at the end of the definition thereof the following:

          "; and minus, for the purposes of calculating Consolidated Total
                 -----
          Adjusted Asset Value only, all interest income of the Borrower, the
          Guarantor and their respective Subsidiaries received in connection
          with any Mortgages."

                                      -5-
<PAGE>
 
6.        The definition of Consolidated Total Adjusted Asset Value is hereby
     amended by deleting the reference to the parenthetical "(a)" in the second
     line of the definition and by deleting subparagraph (iv) of the definition
     in its entirety and inserting the following in place thereof:

                 "(iv) with respect to each Mortgage, the lesser of (y) the
          aggregate amount of principal under such Mortgage that will be due and
          payable to the Borrower or its Subsidiaries (to the extent of
          Borrower's direct or indirect interest therein) and (z) the purchase
          price paid by the Borrower or one of its Subsidiaries to acquire such
          Mortgage. Notwithstanding the foregoing, at any time at which the
          value determined pursuant to this clause (iv) equals or exceeds 10% of
          the total Fair Market Value of Real Estate Assets at such time, then
          upon the occurrence of an event of default under any Mortgage, the
          portion of the value of such defaulted Mortgage which is in excess of
          10% of the total Fair Market Value of Real Estate Assets at such time
          ("Excess Value") shall be reduced to seventy-five percent (75%) of the
          Excess Value as determined in this subparagraph (iv) until the earlier
          to occur of (a) the event of default under the Mortgage is cured in a
          commercially reasonable manner and (b) one hundred eighty (180) days
          after the occurrence of the event of default; thereafter, if the event
          of default under the defaulted Mortgage has not been cured in a
          commercially reasonable manner, the portion of the value of the
          defaulted Mortgage which is in excess of 10% of the total Fair Market
          Value of Real Estate Assets at such time shall be reduced to fifty
          percent (50%) of the Excess Value as determined in accordance with
          this subparagraph (iv) until the earlier to occur of (a) the event of
          default under the Mortgage is cured in a commercially reasonable
          manner and (b) eighteen (18) months after the occurrence of the event
          of default; thereafter, if the event of default under the defaulted
          Mortgage has not been cured in a commercially reasonable manner, the
          portion of the value of the defaulted Mortgage which is in excess of
          10% of the total Fair Market Value of Real Estate Assets at such time
          shall be reduced to zero."

                                      -6-
<PAGE>
 
7.   The definition of Fair Market Value of Real Estate Assets is deleted in its
     entirety and the following is inserted in place thereof:

          "As of any date of determination, the sum of (A) with respect to Real
          Estate Assets other than hotel properties, an amount equal to (i)(x)
          Consolidated EBITDA for the most recent one (1) complete fiscal
          quarter (after adjustments for any straight-line rent accounting),
          minus (y) $.0625 multiplied by the aggregate square footage of all
          -----            ---------- --
          Real Estate Assets other than hotel properties at such date;
          multiplied by (ii) 4; with the product being divided by (iii) the
          ---------- --                                ------- --
          Capitalization Rate, plus (B) with respect to Real Estate Assets which
                               ----
          are hotel properties, an amount equal to (i)(x) Consolidated EBITDA
          for the most recent four (4) consecutive complete fiscal quarters
          (after adjustments for any straight-line rent accounting), minus (y)
                                                                     -----
          the respective Annualized Capital Expenditure for each of the hotel
          properties; divided by (ii) the Capitalization Rate."
                      ------- --

8.        The date specified in the definition of Financial Statement Date of
     "March 31, 1977" is hereby deleted and is replaced with "March 31, 1997."

9.        The definition of Grandfathered Properties is hereby amended by
     deleting each reference to "Total Commitment" contained therein and by
     replacing it with the following:

          "total Borrowing Base Values"

10.       The date specified in the definition of Maturity Date of "June ___,
     2000" is hereby deleted and is replaced with "June 23, 2000."

                                      -7-
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11.       Clause (c) of the first paragraph of Section 9.2 is hereby deleted in
     its entirety and is replaced with the following:

          "(c)  suffer to exist for a period of more than thirty (30) days, with
          respect to the Borrowing Base Properties, any taxes, assessments,
          governmental charges and claims for labor, materials and supplies for
          which payment thereof is not being contested or for which payment
          notwithstanding a contest is required to be made in accordance with
          the provisions of (S)8.9 and has not been timely made and, with
          respect to any individual Borrowing Base Property, is in an amount in
          excess of the lesser of (i) $500,000 and (ii) three percent (3%) of
          the fair market value of the applicable Borrowing Base Property;"

12.       Clause (iv) of the proviso contained in Section 9.2(iv) is amended by
                             -------                                           
     inserting, immediately following the words "the BP Group" contained
     therein, the following:

          "and"

13.       Section 9.3(e) is hereby amended by inserting the words "Real Estate"
     after the words "Fair Market Value of" in the last line of Section 9.3(e).

14.       Section 9.3(f) is hereby amended by inserting the phrase "subject at
     all times to the restrictions of Section 9.7 hereof," at the beginning of
     Section 9.3(f).

15.       Clause (c)(vii) of Section 14.1 is amended to read in its entirety as
     follows:

          "(S)8.13;"

                                      -8-
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16.       Clause (a) of Section 20.1 is amended by inserting, immediately
     following the words "Agent and the Borrower" contained therein, the
     following new words:

          "(other than during an Event of Default)"

17.       Clause (c) of Section 21 is hereby amended by deleting the reference
     to "Schedule 1.3" contained therein and by replacing it with the following:
         ------------
 
          "Schedule 2"
           ---------- 

18.       Clause (vi) of the second paragraph of Section 28 (relating to
     Unanimous Bank Approval) is hereby amended by deleting the period at the
     end thereof and by inserting a semi-colon and the word "or" in place
     thereof.

19.       Section 28 is hereby further amended by inserting the following new
     clause (vii) at the end of clause (vi) of the second paragraph thereof (and
     the remainder of the second paragraph of Section 28 shall become a new
     third paragraph):

          "(vii) changes the liability of the Guarantor under the Guaranty or
          has the effect of releasing the Guaranty."

20.       Clause (i) of the third paragraph of Section 28 (relating to Required
     Banks) is hereby deleted in its entirety and is replaced with the
     following:

          "(i) amends any of the covenants contained in (S)10.1 through (S)10.7,
          inclusive, or amends any of the definitions which are financial terms
          contained therein, or"

21.       All capitalized terms not otherwise defined herein shall have the
     meanings given to them in the Credit Agreement.

22.       Except as specifically amended by the terms of this First Amendment,
     all of the terms, conditions and provisions of the Credit Agreement and the
     other Loan Documents shall remain in full force and 

                                      -9-
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     effect through the balance of the term of the Credit Agreement. From and
     after the date hereof, the Credit Agreement and this Amendment shall
     collectively be referred to as the "Credit Agreement."

                                      -10-
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     WITNESS the execution hereof, under seal, in any number of counterpart
copies, each of which counterpart copy shall be deemed an original for all
purposes, as of the day and year first written above.

[Signature pages omitted.  Executed by the following parties:]

                               BANKBOSTON, N.A., individually and as Agent
                                                                          
                               THE ATLANTIC MONTHLY TRUST                 
                                                                          
                               MBZ-LEX TRUST                              
                                                                          
                               ZEE EM TRUST II                            
                                                                          
                               WP TRUST                                   
                                                                          
                               TRACER LANE TRUST                          
                                                                          
                               HAYDEN OFFICE TRUST                        
                                                                          
                               ELANDZEE TRUST                             
                                                                          
                               ZEE BEE TRUST II                           
                                                                          
                               ONE CAMBRIDGE CENTER TRUST                 
                                                                          
                               THREE CAMBRIDGE CENTER TRUST               
                                                                          
                               ELEVEN CAMBRIDGE CENTER TRUST              
                                                                          
                               FOURTEEN CAMBRIDGE CENTER TRUST             

                                      -11-
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                               SCHOOL STREET ASSOCIATES LIMITED PARTNERSHIP

                               DEMOCRACY ASSOCIATES LIMITED PARTNERSHIP

                               MARYLAND 50 BUILDING I ASSOCIATES 
                                   LIMITED PARTNERSHIP

                               MARYLAND 50 BUILDING II ASSOCIATES 
                                   LIMITED PARTNERSHIP

                               MARYLAND 50 BUILDING III ASSOCIATES 
                                   LIMITED PARTNERSHIP

                               DOWNTOWN BOSTON PROPERTIES TRUST

                               TWO CAMBRIDGE CENTER TRUST

                               BOSTON PROPERTIES LIMITED PARTNERSHIP

                               BOSTON PROPERTIES, INC.,
                               as Guarantor

                                      -12-
