<PAGE>

                                                                    EXHIBIT 99.1

                                    SPSS INC.
            CHARTER OF THE AUDIT COMMITTEE OF THE BOARD OF DIRECTORS

1.     Purpose of the Charter.

       The purpose of this Charter (the "Charter") of the Audit Committee (the
       "Committee") of the Board of Directors (the "Board") of SPSS Inc. (the
       "Company") is to establish membership requirements for the Committee and
       to assist the Committee in complying with its duties under applicable
       law.

2.     Committee Composition.

       (a)    Composition.  The Committee shall consist of at least three (3)
              members of the Board who satisfy the requirements of the Sarbanes-
              Oxley Act of 2002 (the "Act"), the rules promulgated by the
              Securities and Exchange Commission (the "SEC") in connection with
              the Act and the rules promulgated for companies listed on the
              NASDAQ National Market.

       (b)    Appointment; Removal.  The Committee members shall be appointed by
              the Board, upon the recommendation of the Nominating Committee of
              the Board, to serve for a one (1) year term or until their
              successors shall be duly elected and qualified. Each Committee
              member may be removed by the Board in its sole discretion.

       (c)    Membership Requirements.  Each Committee member must:

              (i)    qualify as an "independent" director under the rules
                     applicable to companies listed on the NASDAQ National
                     Market;

              (ii)   meet the criteria for audit committee independence set
                     forth in Rule 10A-3 promulgated pursuant to the Securities
                     Exchange Act of 1934;

              (iii)  not have participated in the preparation of the financial
                     statements of the Company or any current subsidiary of the
                     Company at any time during the past three years; and

              (iv)   be financially literate, including without limitation, able
                     to read and understand fundamental financial statements,
                     including the Company's balance sheet, income statement and
                     cash flow statement.

       (d)    Financial Expert.  The Committee shall designate at least one of
              its members as a financial expert (the "Financial Expert"). Prior
              to designating a Committee member as a Financial Expert, the
              Committee must make a determination that the individual so
              designated is financially sophisticated. Financial sophistication
              may be demonstrated by past employment experience in finance or
              accounting, professional certification in accounting or other
              comparable experience or background, including current or past
              employment as a chief executive officer, chief financial officer
              or other senior financial officer with financial oversight
              responsibilities. A director who qualifies as an audit committee
              financial expert under Item 401 of Regulation S-K is presumed to
              qualify as financially sophisticated.

       (e)    Committee Chairman.  The Board may designate a chairman of the
              Committee. If the Board does not designate a Chairman, the
              Committee members shall elect a Chairman by a vote of a majority
              of the Committee.

3.     Committee Meetings

       (a)    In order to satisfy its obligation to oversee the accuracy and
              adequacy of the Company's financial reporting and disclosures, the
              Committee shall meet each quarter prior to the publication of the
              Company's quarterly earnings release. The Committee shall convene
              such number of additional meetings at such times as are necessary
              or appropriate to allow the Committee to fully discharge its
              duties and responsibilities as set forth herein. Each Committee
              member and either of the Company's Chief Executive Officer or
              Chief Financial Officer shall have the authority to call a meeting
              of the

<PAGE>

            Committee. The notice of meeting need not state the purpose for
            which the meeting has been called. In order to transact business, at
            least two (2) Committee members must be present.

      (b)   The Chairman shall be responsible for establishing the agenda for
            each meeting and will coordinate the distribution of briefing and/or
            background material to the Committee members. Additional items may
            be added to the agenda at the request of any Committee member.
            Minutes of all meetings shall be prepared by or under the
            supervision of the Chairman and approved by the Committee. Meetings
            may be held via conference call or in person.

      (c)   The Committee shall meet periodically as necessary, but no less than
            annually, with management, the director of the internal auditing
            department and the independent auditors and as a Committee in
            separate executive sessions to discuss matters that the Committee,
            or any of these persons, believe should be discussed. The Committee,
            or at least its chairman, should communicate with management and the
            independent auditors quarterly to review the Company's financial
            statements and significant findings based upon the auditor's limited
            review procedures.

4.     Authority

       The Committee is empowered to:

       (a)    Do all things necessary to fully discharge its duties as described
              herein.

       (b)    Engage independent counsel, accountants and other advisers, as it
              determines necessary to carry out the responsibilities and duties
              of the Committee. The Committee shall inform the Board of any
              proposed engagement prior to such engagement.

       (c)    Conduct or authorize any investigations into any matters within
              the Committee's scope of responsibilities.

       (d)    Seek any information required by the Committee from employees (all
              of whom are directed to cooperate with the Committee's requests)
              or external parties.

       (e)    Meet with Company officers, external auditors, or outside counsel,
              as necessary.

       (f)    Pre-approve all audit and permitted non-audit services performed
              by the Company's independent auditor. Delegate pre-approval
              authority to one or more designated members, provided that such
              decisions are presented to the full Committee for ratification at
              its next scheduled meeting.

5.     Responsibilities and Duties

       The Audit Committee shall have the following responsibilities and duties:

       (a)    Internal Accounting Matters

              (i)    Internal Controls

                     (A)    Consider the effectiveness and integrity of the
                            Company's internal controls over financial reporting
                            and reporting system, including information
                            technology security and control.

                     (B)    Understand the scope of internal and external
                            auditors' review of the Company's internal controls
                            over financial reporting, and obtain reports on
                            significant findings and recommendations, together
                            with management's responses.

                     (C)    Review disclosures made by the Company's Chief
                            Executive Officer and Chief Financial Officer in
                            connection with the periodic report certification
                            process regarding significant deficiencies in the
                            design or operation of the Company's internal
                            controls over financial reporting or any fraud that
                            involves management or other employees who have a
                            significant role in the Company's internal controls.

                     (D)    Review, approve and monitor compliance with the
                            Company's Code of Business Conduct and Ethics which
                            includes the Code of Ethics for its Chief Executive
                            Officer, Chief Financial Officer and other senior
                            financial officers.

<PAGE>

              (ii)   Internal Audit

                     (A)    Review and approve the Company's internal audit
                            staff functions, including authority and
                            organizational reporting lines as well as the annual
                            audit plan and budget. Review the effectiveness of
                            the Company's internal audit function, including
                            compliance with all applicable standards for
                            internal auditors.

                     (B)    Meet with the Company's chief audit executive on a
                            regular basis to ensure adequate oversight of the
                            internal audit function.

              (iii)  Compliance and Risk Management

                     (A)    Discuss policies with respect to risk assessment and
                            risk management, including the Company's major
                            financial risk exposures and the steps taken by
                            management to monitor, control, mitigate and report
                            such exposures.

                     (B)    Review the effectiveness of the system for
                            monitoring compliance with laws and regulations and
                            the results of management's investigation and
                            follow-up (including disciplinary action) of any
                            instances of noncompliance.

                     (C)    Review the findings of any examination by regulatory
                            agencies, and any auditor observations.

                     (D)    Obtain regular updates from management and the
                            Company's legal counsel regarding compliance matters
                            that may have a material affect on the financial
                            performance of the Company or on the Company's
                            financial statements or reporting obligations.

       (b)    External Audit

              (i)    The Committee has exclusive authority and responsibility to
                     appoint, direct, oversee and either retain or terminate the
                     Company's independent auditors.

              (ii)   In exercising its authority with respect to the Company's
                     independent auditor, the Audit Committee shall:

                     (A)    Review and approve the scope, fees and terms of each
                            audit engagement, which review shall include,
                            without limitation, a review of the independent
                            auditor's audit plan and matters related to
                            staffing, reliance upon management and the internal
                            audit and general audit approach.

                     (B)    At least annually, obtain and review a report by the
                            independent auditor describing: (i) the firm's
                            internal quality-control procedures; (ii) any
                            material issues raised by the most recent internal
                            quality-control review, or peer review, of the firm,
                            or any inquiry or investigation by governmental or
                            professional authorities, within the preceding five
                            years, respecting one or more independent audits
                            carried out by the firm, and any steps taken to deal
                            with such issues; and (iii) all relationships
                            between the independent auditor and the Company.

                     (C)    Evaluate the independent auditor's qualifications,
                            experience, performance, and independence, taking
                            into account the opinions of management and the
                            Company's internal auditors.

                     (D)    Review and evaluate the lead partner and manager of
                            the independent auditor and assure the rotation of
                            the lead audit partner every five (5) years, and
                            other audit partners every seven (7) years, and
                            other audit personnel as required by law, and
                            consider whether there should be regular rotation of
                            the audit firm itself.

                     (E)    Present its conclusions on the performance of the
                            independent auditor to the Board.

              (iii)  Review and approve or veto the Company's hiring of
                     employees or former employees of the Company's independent
                     auditor who participated in any capacity in the audits of
                     the Company.

<PAGE>

              (iv)   Meet with the independent auditors on a regular basis to
                     discuss any matters that the Committee or independent
                     auditors believe should be discussed privately.

              (v)    Resolve disagreements between the independent auditors,
                     management and the Company's internal auditing staff
                     regarding issues relating to accounting standards,
                     financial reporting, the preparation of the Company's
                     financial statements and periodic reports or such other
                     related issues that the Committee deems to be within its
                     purview.

       (c)    Financial Statements

              (i)    Review the Company's annual audited financial statements
                     and quarterly financial statements with management,
                     internal auditors and the independent auditors before
                     distributing or filing with regulators, and consider
                     whether they are complete, consistent with information
                     known to Committee members, and reflect appropriate
                     accounting principles. This review should include
                     discussion with management and the Company's independent
                     auditors regarding significant issues related to accounting
                     principles, practices and judgments.

              (ii)   Review the Company's periodic reports before they are filed
                     with the SEC. This review should include discussion with
                     management and the Company's independent auditors regarding
                     the Company's disclosures under "Management's Discussion
                     and Analysis of Financial Condition and Results of
                     Operations."

              (iii)  Review significant accounting and reporting issues,
                     including complex or unusual transactions and highly
                     judgmental areas as well as any significant changes in the
                     Company's selection or application of accounting principles
                     and recent professional and regulatory pronouncements, and
                     understand their impact on the financial statements.

              (iv)   Review with the independent auditors the results of the
                     audit and any audit problems or difficulties and
                     management's response. This review will include any
                     restrictions on the scope of the independent auditor's
                     activities or on access to requested information, and any
                     significant disagreement with management.

              (v)    Discuss the Company's earnings press releases (particularly
                     the use of "pro-forma," or "adjusted" non-GAAP,
                     information), as well as financial information and earnings
                     guidance provided to analysts and rating agencies. This
                     review may be general (i.e., the types of information to be
                     disclosed and the type of presentations to be made). The
                     Company shall discuss any press release which contains
                     financial information with the Committee chair prior to
                     release. However, the Committee is not required to discuss
                     and/or approve each release in advance.

              (vi)   Receive and review (A) reports of the independent auditor
                     regarding critical accounting policies and practices to be
                     used, (B) all material alternative treatments of financial
                     information within generally accepted accounting principles
                     that have been discussed with management and the
                     ramifications of using such alternative treatments, (C) the
                     reasonableness of all material estimates and judgments made
                     by the Company in the preparation of its financial
                     statements and (D) other material written communications
                     between the independent auditor and management, including
                     any management representation letter, report on
                     observations and recommendations on internal controls,
                     schedule of unadjusted differences, and a listing of
                     adjustments and reclassifications not recorded. Assess the
                     quality, not just the acceptability, of the Company's
                     accounting principles and financial disclosure practices
                     used or proposed and the appropriateness of significant
                     management judgments.

       (d)    Reporting Responsibilities

              (i)    Regularly report to the Board about Committee activities
                     and issues that arise with respect to the quality or
                     integrity of the Company's financial statements, the
                     Company's compliance with legal and regulatory
                     requirements, the performance and independence of the
                     Company's independent auditors, and the performance of the
                     internal audit function.

<PAGE>

              (ii)   Provide an open avenue of communication between internal
                     auditors, the external auditors, management and the Board.

              (iii)  Prepare and publish an annual committee report in the
                     Company's proxy filing which report shall satisfy the
                     requirements of the Securities Exchange Act of 1934. This
                     report shall describe, among other things, the Committee's
                     composition, responsibilities and how they were discharged,
                     and any other information required by law or rule,
                     including approval of non-audit services.

              (iv)   Review any other reports the Company issues that relate to
                     Committee responsibilities.

              (v)    Report all material findings and all recommendations that
                     may arise at a meeting of the Committee to the entire
                     Board. Such report shall be made at the Board meeting
                     immediately following the relevant Committee meeting.

       (e)    Complaints and Concerns

              (i)    Establish procedures for the receipt, retention and
                     treatment of complaints received by the Company regarding
                     accounting, internal accounting controls or auditing
                     matters.

              (ii)   Establish and make known procedures for the confidential,
                     anonymous submission by employees of the Company of
                     concerns regarding questionable accounting or auditing
                     matters.

              (iii)  Implement and enforce protections for lawful employee
                     actions regarding complaints and submissions under the
                     above procedures.

       (f)    Other Responsibilities

              (i)    Review and approve, as may be required by NASDAQ National
                     Market, related party transactions and conflicts of
                     interest questions between Board members or management, on
                     the one hand, and the Company, on the other hand.

              (ii)   Perform an annual evaluation of the Committee and the
                     performance of its individual members.

              (iii)  Review and assess the adequacy of this Charter annually, or
                     more frequently as required by law, requesting Board
                     approval for proposed changes, and ensure appropriate
                     disclosure as may be required by law or regulations. Have
                     this Charter published at least every three (3) years in
                     accordance with SEC regulations. Perform other activities
                     related to this Charter as requested by the Board.

              (iv)   Investigate any other matter brought to its attention
                     within the scope of its duties which it deems appropriate
                     for investigation.

              (v)    Perform any other activities consistent with this Charter,
                     the Company's Certificate of Incorporation or By-laws and
                     any other governing law, as the Committee or the Board
                     deems necessary or appropriate.

6.     Scope

       While the Committee has the responsibilities and authority set forth in
       this Charter, it is not the duty of the Committee to prepare the
       Company's financial statements, to certify that the Company's financial
       statements and disclosures are completely accurate and are in accordance
       with generally accepted accounting principles and applicable rules and
       regulations, to plan or conduct the audit or to guarantee the independent
       auditor's report. These are the responsibilities of management and the
       independent auditor. The Committee is charged with the oversight roles
       for these functions as set out in this Charter.