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                                                                    EXHIBIT 31.1


                          RULE 13A-14(A) CERTIFICATION

                             SIMULATIONS PLUS, INC.
                            a California corporation

                    CERTIFICATION OF CHIEF EXECUTIVE OFFICER

         I, Walter S. Woltosz, Chief Executive Officer of Simulations Plus,
Inc., a California corporation (the "Company"), do hereby certify, in accordance
with Rules 13a-14 and 15d-14, as created pursuant to Section 302(a) of the
Sarbanes-Oxley Act of 2002, with respect to the Quarterly Report on Form 10-QSB
of the Company for the fiscal quarter ended May 31, 2008, as filed with the
Securities and Exchange Commission herewith under Section 15(d) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), that:

        (1) I have reviewed this Quarterly Report on Form 10-QSB of the Company
            for the fiscal quarter ended May 31, 2008 (the "Quarterly Report");

        (2) Based on my knowledge, this Quarterly 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 Quarterly Report;

        (3) Based on my knowledge, the financial statements, and other financial
            information included in this Quarterly Report, fairly present in all
            material respects the financial condition, results of operations and
            cash flows of the Company as of, and for, the periods presented in
            this Quarterly Report;

        (4) The Company's other certifying officers and I are responsible for
            establishing and maintaining disclosure controls and procedures (as
            defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal
            controls over financial reporting (as defined in Exchange Act Rules
            13a-15(f) and 15(d)-15(f)) for the Company 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 Company, including its consolidated
                    subsidiaries, is made known to us by others within those
                    entities, particularly during the period in which this
                    Quarterly Report is being prepared;

                (b) designed such internal controls over financial reporting, or
                    caused such internal controls 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 Company's disclosure
                    controls and procedures and presented in this Quarterly
                    Report our conclusions about the effectiveness of the
                    disclosure controls and procedures, as of the end of the
                    period covered by this Quarterly Report based on such
                    evaluation; and

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                (d) disclosed in this Quarterly Report any change in the
                    Company's internal controls over financial reporting that
                    occurred during the Company's most recent fiscal quarter
                    (the Company's fourth fiscal quarter in the case of an
                    annual report) that has materially affected, or is
                    reasonably likely to materially affect, the Company's
                    internal controls over financial reporting; and

        (5) The Company's other certifying officers and I have disclosed, based
            on our most recent evaluation, to the Company's auditors and the
            audit committee of the Company's board of directors (or persons
            performing the equivalent functions):

                (a) all significant deficiencies and material weaknesses in the
                    design or operation of internal controls over financial
                    reporting which are reasonably likely to adversely affect
                    the Company'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
                    Company's internal controls over financial reporting.


Dated: July 14, 2008                               By: /s/ Walter S. Woltosz
                                                       ---------------------
                                                       Walter S. Woltosz
                                                       Chief Executive Officer