Decision Support Systems (DSSs) are computer-based information systems for providing necessary supports for business or organizational decision-making activities. DSSs often serve the management, operations, and planning levels of all organizations and help to make decisions, which may be rapidly changing and not easily achieved in advance. This paper presents an empirical investigation to find important factors influencing DSSs. The proposed study designs a questionnaire in Likert scale consists of 36 questions, distributes it among 213 employees who work for different offices in municipality of Tehran, Iran. Cronbach alpha is calculated as 0.872. In addition, Kaiser-Meyer-Olkin Measure of Sampling Adequacy and Approx. Chi-Square are 0.782 and 1014.521, respectively. Based on the results of our survey, we have derived three factors including system, analysis and transaction.