<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 one of its members as
a financial expert (the "Financial Expert"). Prior to designating the 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
<PAGE>

Financial Officer shall have the authority to call a meeting of the 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.

                                        2
<PAGE>

          (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.

          (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.

                                        3
<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.

                                        4
<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.

                                        5