Research Problem: 45-65% of all medical supplies in hospital are used in operating rooms. Medical supplies in operating rooms are difficult to manage in general because many of them are frequently used and come in a variety of types. Purpose: Our aim was to strive for user-friendliness and reduce the inventory through efficient management of medical supplies stocked in operating rooms. Medical Facility: Korea University, Ansan Hospital Quality Improvement Activity: On the last day of each month, we checked the inventory of medical supplies in all operating rooms by identifying the amount of medical supplies in each room, warehouse, and OCS, identified problems, and presented the ways to improve. Improvement Outcome: We increased the number of post-processing medical supply items by 8%, and reduced the inventory cost by 15% through improved management of medical supplies.