In RFID system, one of the problems that we must solve is the collision between tags which lowers the efficiency of the RFID system. One of the popular anti-collision algorithms is ALOHA-type algorithms, which are simple and shows good performance when the number of tags to read is small. However, they generally require exponentially increasing number of slots to identify the tags as the number of tag increases. In the paper, we propose a new anticollision algorithm called Enhanced Dynamic Framed Slotted ALOHA (EDFSA) which estimates the number of unread tags first and adjusts the number of responding tags or the frame size to give the optimal system efficiency. As a result, in the proposed method, the number of slots to read the tags increases linearly as the the number of tags does. Simulation results show that the proposed algorithm improves the slot efficiency by 85~100% compared to the conventional algorithms when the number of tags is 1000.