This study aims at the development of a cost management system in building interior projects. Renovation and remodeling is activated and expanded much more being compared with new building construction at present. After Interior project proceeding must get out of simple estimate and assumption, then its be needed a formal work process and computerized cost management. Proceeding a building interior project management was proceed in the office and the field. Cost break down, especially, depend on the field manger and used fiend managing money because its not checked by cost manager in office manger. For this study, cost factors are defined in terms of cost break-down interior works which consist of materials and labors. A data model for cost factors was developed, and a relational database is used to realize cost data management based upon this data model. Data input and output are achieved by internet from both of wired PC and mobile phone. This system can timely display a number of needed reports for cost management that identifies cash flow and predicts budget for cost break-down works in interior projects.