An inventory management affects carrying cost, ordering cost, and shortage cost.  So, success in business management must be considered the good inventory management system, especially the Small Medium Enterprise (SME).  The effective categorization of materials is also important to prioritize and optimize inventory management which the material disbursement in the warehouse system more efficient. In this study, the cause of the problems was analyzed by Fishbone Diagram. It was found the main cause of the ordering cost was because the inventory was unclassified.   Then, the ABC Classification was used to classify the material product groups. For all groups (ABC) use the Economic Order Quantity model for order quantity planning.   After implementation, the total cost of group A was reduced by THB 128,737 per year. Group B was reduced by THB 76,982 per year and group C was reduced by THB 122,757 per year.