The development of a UIS driven by muncipal governments has been expanding through the wide application of GIS since NGIS project initiated. City of Inchon has developed a sewage management system as the first-year product of the long-term UIS project. GIS auditing process has been adopted to secure the credibility and stability, and to minimize the critical failure factors for building the sewage management system. So far, the auditing method generally used for developing information system in general purposes has been applied to the GIS field due to the absence of proper method for GIS auditing only. This study proposes major differentials in terms of the auditing between GIS and general information system based on the results from auditing Inchon´s sewage management system. The major results from this study would contribute to the establishment of the methodology and accompanying documents for the proper GIS auditing.