In this paper, we propose a method that manages gateway readers in the warehouse efficiently. The basic role of gateway readers is to identify products coming in and out. Therefore, an efficient management method of gateway readers is required to improve the speed of tag identification process and reduce the number of used readers. Our proposed management method for gateway readers is based on the reuse of gateway readers. Therefore, when both products coming in and out will pass through this single gateway installed with some RFID readers, the readers can distinguish whether they are coming in or out. We examine the performance of proposed management method for gateway readers by using GEN2 simulator. As a result, we can reduce the number of readers about 62.5%, compared with the ones without any reuse.