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                                                                    Exhibit 4.5
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                             ASPEN TECHNOLOGY, INC.

                             1995 STOCK OPTION PLAN


     1.   DEFINITIONS. As used in this 1995 Stock Option Plan of Aspen 
Technology, Inc., the following terms shall have the following meanings:

          1.1 CHANGE IN CORPORATE CONTROL means the date on which any
     individual, corporation, partnership or other person or entity (together
     with its "Affiliates" and "Associates," as defined in Rule 12b-2 under the
     Securities Exchange Act of 1934) "beneficially owns" (as defined in Rule
     13d-3 under the Securities Exchange Act of 1934) in the aggregate 20% or
     more of the outstanding shares of capital stock of the Company entitled to
     vote generally in the election of directors of the Company.

          1.2 CODE means the Internal Revenue Code of 1986, as amended.

          1.3 COMMITTEE means the Compensation Committee of the Company's Board
     of Directors.

          1.4 COMPANY means Aspen Technology, Inc., a Massachusetts corporation.

          1.5 FAIR MARKET VALUE means the value of a share of Stock of the
     Company on any date as determined by the Committee.

          1.6 GRANT DATE means the date on which an Option is granted, as
     specified in Section 7.

          1.7 INCENTIVE OPTION means an option which qualifies for tax treatment
     under Section 422 of the Code.

          1.8 MAJOR SHAREHOLDER means a person who, within the meaning of
     Section 422(b)(6) of the Code, is deemed to own stock possessing more than
     10% of the total combined voting power of all classes of stock of the
     Company (or of its parent or subsidiary corporations).



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          1.9  OPTION means an option to purchase shares of the Stock granted
     under the Plan.

          1.10 OPTION AGREEMENT means an agreement between the Company and an
     Optionee, setting forth the terms and conditions of an Option.

          1.11 OPTION PRICE means the price paid by an Optionee for an Option
     under this Plan.

          1.12 OPTION SHARE means any share of Stock of the Company transferred
     to an Optionee upon exercise of an Option pursuant to this Plan.

          1.13 OPTIONEE means a person eligible to receive an Option, as
     provided in Section 6, to whom an Option shall have been granted under the
     Plan.

          1.14 PLAN means this 1995 Stock Option Plan of the Company.

          1.15 RELATED CORPORATION means a Parent Corporation or a Subsidiary
     Corporation, each as defined in Section 424 of the Code.

          1.16 STOCK means common stock, $.10 par value, of the Company.

     2.   PURPOSE. This 1995 Stock Option Plan is intended to encourage 
ownership of the Stock by key employees and key advisors of the Company and its
Related Corporations and to provide additional incentive for them to promote the
success of the Company's business. The Plan is intended to be an incentive stock
option plan within the meaning of Section 422 of the Code, but not all the
Options must be Incentive Options.

     3.   TERM OF THE PLAN. Options under the Plan may be granted not later than
November 30, 2005.

     4.   STOCK SUBJECT TO THE PLAN. Subject to the provisions of Section 16 of
the Plan, the number of shares of the Stock attributable to the exercise of
Options granted under the Plan plus the number of shares then issuable upon
exercise of outstanding options granted under the Plan shall at no time exceed
800,000 increased automatically at each of July 1, 1996 and July 1, 1997 by an

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amount equal to 5% of the Stock outstanding on the preceding June 30. Unless and
until the Plan is amended, however, at no time may the number of shares
purchaseable under Options which are Incentive Options exceed 2 million shares.
Shares to be issued upon the exercise of Options granted under the Plan may be
either authorized but unissued shares or shares held by the Company in its
treasury. If any Option expires or terminates for any reason without having been
exercised in full, the shares not purchased thereunder shall again be available
for Options thereafter to be granted.

     5.   ADMINISTRATION. The Plan shall be administered by the Committee. 
Subject to the provisions of the Plan, the Committee shall have complete
authority, in its discretion, to make the following determinations with respect
to each Option to be granted by the Company: (a) the key employee or key advisor
to receive the Option; (b) the time of granting the Option; (c) the number of
shares subject thereto; (d) the Option Price; (e) the Option period; and (f) if
the Optionee is an employee, whether the Option is an Incentive Option. In
making such determinations, the Committee may take into account the nature of
the services rendered by the key employees and key advisors, their present and
potential contributions to the success of the Company and its Related
Corporations, and such other factors as the Committee in its discretion shall
deem relevant. Subject to the provisions of the Plan, the Committee shall also
have complete authority to interpret the Plan, to prescribe, amend and rescind
rules and regulations relating to it, to determine the terms and provisions of
the respective Option Agreements (which need not be identical), and to make all
other determinations necessary or advisable for the administration of the Plan.
The Committee's determinations on the matters referred to in this Section 5
shall be conclusive.

     6.   ELIGIBILITY. An Option may be granted only to a key employee or key
advisor of one or more of the Company and its Related Corporations. A director
of one or more of the Company and its Related Corporations who is not also an
employee of one or more of the Company and its Related Corporations shall not be
eligible to receive an Option. A Major Shareholder shall be eligible to receive
an Incentive Option only if the Option Price is at least 110% of the Fair Market
Value on the Grant Date and only if the Incentive Option expires, to the extent
not theretofore exercised, on the fifth anniversary of the Grant Date.

     7.   TIME OF GRANTING OPTIONS. The granting of an Option shall take place 
at the time specified by the Committee. Only if expressly so provided by the
Committee, shall the Grant Date be the date on which an Option Agreement shall
have been duly executed and delivered by the Company and the Optionee.

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     8.   OPTION PRICE. The Option Price under each Incentive Option shall be 
not less than 100% of the Fair Market Value of the Stock on the Grant Date
except that the Option Price under an Incentive Option granted to a Major
Shareholder must be not less than 110% of the Fair Market Value.

     9.   OPTION PERIOD. No Option may be exercised later than the tenth
anniversary of the Grant Date or, for an Incentive Option granted to a Major
Shareholder, the fifth anniversary of the Grant Date. Unless the Committee
otherwise determines, all Options granted hereunder shall permit the Optionee to
purchase, cumulatively, one-sixteenth of the Option Shares at the end of each
calendar quarter following the Grant Date. Upon a Change in Corporate Control,
each outstanding Option shall immediately become fully exercisable.

     10.  MAXIMUM SIZE OF OPTION. No person shall be granted Options to purchase
more than 500,000 shares of Stock. To the extent that the aggregate Fair Market
Value of Stock for which an Incentive Option becomes exercisable by an Optionee
for the first time in any calendar year exceeds $100,000, the Option shall be
treated as a nonstatutory option, and not an Incentive Option. For purposes of
this Section 10, all Options granted to an Optionee by the Company shall be
considered in the order in which they were granted, and the Fair Market Value
shall be determined as of the Grant Dates.

     11.  EXERCISE OF OPTION. An Option may be exercised only by giving written
notice, in the manner provided in Section 20 hereof, specifying the number of
shares as to which the Option is being exercised, accompanied by (a) full
payment for such shares in the form of check or bank draft payable to the order
of the Company, or (b) certificates representing shares of the Stock with a
current Fair Market Value equal to the Option Price of the shares to be
purchased, or (c) irrevocable instructions to a brokerage firm to sell a
sufficient number of the Option Shares to generate the full exercise price plus
all applicable withholding taxes and to pay over to the Company such proceeds of
sale. Receipt by the Company of such notice and payment shall constitute the
exercise of the Option or a part thereof. The Company shall thereafter deliver
or cause to be delivered to the Optionee a certificate or certificates for the
number of shares then being purchased by the Optionee. Such shares shall be
fully paid and nonassessable. If any law or applicable regulation of the
Securities and Exchange Commission or other body having jurisdiction in the
premises shall require the Company or the Optionee to take any action in
connection with shares being purchased upon exercise of the option, exercise of
the option and delivery of the certificate or certificates for such shares shall
be postponed until completion of the necessary action, which shall be taken at
the Company's expense.

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     12.  NOTICE OF DISPOSITION OF STOCK PRIOR TO EXPIRATION OF SPECIFIED 
HOLDING PERIOD. The Company may require that the person exercising an Incentive
Option give a written representation to the Company, satisfactory in form and
substance to its counsel and upon which the Company may reasonably rely, that he
or she will report to the Company any disposition of shares purchased upon
exercise prior to the expiration of the holding periods specified by Section
422(a)(1) of the Code. If and to the extent that the disposition imposes upon
the Company federal, state, local or other withholding tax requirements, or any
such withholding is required to secure for the Company an otherwise available
tax deduction, the Company shall have the right to require that the person
making the disposition remit to the Company an amount sufficient to satisfy
those requirements.

     13.  TRANSFERABILITY OF OPTIONS. Options shall not be transferable,
otherwise than by will or the laws of descent and distribution, and may be
exercised during the life of the Optionee only by the Optionee.

     14.  STOCK PURCHASE AGREEMENT Each Optionee exercising an option, at the
request of the Company, will be required to sign a Stock Purchase Agreement
representing in form satisfactory to counsel for the Company that he or she will
not transfer, sell or otherwise dispose of the Option Shares at any time
purchased by him or her, upon the exercise of any portion of the Option, in a
manner which would violate the Securities Act of 1933, as amended, and the
regulations of the Securities and Exchange Commission thereunder; and the
Company may, at its discretion, make a notation on any certificates issued upon
exercise of options to the effect that such certificate may not be transferred
except after receipt by the Company of an opinion of counsel satisfactory to it
to the effect that such transfer will not violate such Act and such regulations,
and may issue "stop transfer" instructions to its transfer agent, if any, and
make a "stop transfer" notation on its books as appropriate. Such Stock Purchase
Agreement shall include such other provisions as the Committee may determine are
appropriate.

     15.  TERMINATION OF EMPLOYMENT. In the event that the Optionee's employment
is terminated for any reason other than death or the Optionee's employer is no
longer the Company or a Related Corporation, the Option, to the extent
exercisable at termination, may be exercised by the Optionee at any time within
30 days after termination unless terminated earlier by its terms. If termination
results from the death of the Optionee, the Option, to the extent exercisable at
the date of death, may be exercised by the person to whom the Option is
transferred by will or the applicable laws of descent and distribution, at any
time within 12 months after the date of death, unless terminated earlier by its
terms. Military or sick leave shall not be deemed a termination of employment
provided that it does not exceed the longer of 90 days or the 

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period during which the absent employee's re-employment rights are guaranteed by
statute or by contract.

     16.  ADJUSTMENT OF NUMBER OF SHARES. Each Option Agreement shall provide
that in the event of any capital adjustments including stock splits, stock
contractions, stock dividends, reclassifications, exchanges and substitutions,
occurring after the date of the option and prior to the exercise in full of the
option, the number of shares for which the option may be exercised and the price
per share shall be proportionately adjusted and in the event of any resulting
changes in the outstanding Stock, the number of shares of the Stock available
for the purpose of the Plan as stated in Section 4 hereof shall be
correspondingly adjusted. 

     17.  STOCK RESERVED. The Company shall at all times during the term of the
Option reserve and keep available such number of shares of the Stock as will be
sufficient to satisfy the requirements of this Plan and shall pay all fees and
expenses necessarily incurred by the Company in connection therewith.

     18.  LIMITATION OF RIGHTS IN THE OPTION SHARES. An Optionee shall not be
deemed for any purpose to be a stockholder of the Company with respect to any of
the Option Shares except to the extent that the Option shall have been exercised
with respect thereto and, in addition, a certificate shall have been issued
therefor and delivered to the Optionee.

     19.  TERMINATION AND AMENDMENT OF THE PLAN. The Board of Directors of the
Company may at any time terminate the Plan or make such amendment to the Plan as
it shall deem advisable, provided that, except as provided in Section 16, it may
not, without the approval by the holders of a majority of the Stock, change the
classes of persons eligible to receive Options, increase the maximum number of
shares available for option under the Plan or extend the period during which
Options may be granted or exercised. No termination or amendment of the Plan
may, without the consent of the Optionee to whom any Option shall theretofore
have been granted, adversely affect the rights of such Optionee under such
Option. The Company may also, in its discretion, permit any option to be
exercised prior to the date on which it vests.

     20.  NOTICES. Any communication or notice required or permitted to be given
under the Plan shall be in writing, and mailed by registered or certified mail
or delivered in hand, if to the Company, to its Chief Financial Officer at Ten
Canal Park, Cambridge, MA 02141 and, if to the Optionee, to the address as the
Optionee shall last have furnished to the Company.