Warehouse Management System is a database-based computer application system, which used to improve warehouse efficiency in maintaining the accuracy of inventory data by recording every transaction in the warehouse. The purpose of this study was to determine efficiency of material handling costs incurred after implementation of warehouse management system. The research was conducted at PT Uniplastindo Interbuana Bali with simulation of implementation warehouse management system. Based on calculations, application of WMS able to increase cost efficiency and time efficiency in material handling because the system is able to provide accurate material placement data. Data during simulation shows a smaller amount of time compared to before simulation, which means less costs are incurred. Existence of system also makes it easy for related admin to collect data on real stock in the field. Data presentation and processing becomes faster and accurate so it can lead to increased performance in company. Keywords: Warehouse Management System (WMS), material handling, cost efficiency