This final project discusses the application design of sales, purchase, and inventory of Toko Semeru. The conventional system of Toko Semeru causes reoccurring problems that are a disadvantage to their business because of the daily record inaccuracies they generate. The computerized sales, purchase, and inventory system of Toko Semeru is the main focus in this project. The analysis phase includes requirement gathering through interview, document analysis, and observation. The system is designed by applying the prototyping methodology The business process are modeled by using Unified Modeling Language (UML) diagrams. The database system is developed using the Microsoft SQL Server and the application is developed by using Microsoft Visual Basic The system will be able to manage the data of the transaction process, the managing inventory, and the information of products, suppliers, customers, employees, and stocks. It can also eliminate the weaknesses which are discovered in the previous system of daily operation.