RFID systems have emerged as an affordable solution for identifying physical objects. However several problems still remain unresolved, especially avoidance of collision (anti-collision algorithm) when identifying multiple tags simultaneously. This paper presents an efficient anti-collision algorithm based on stochastic method. The algorithm we propose uses bit-slot mechanism. Bit-slot mechanism means the way that regards one bit of each tag as one time slot. Compared to other stochastic algorithms such as I-Code protocol, the proposed algorithm does not need any timing circuit with tags while I-Code protocol needs one. Moreover, it decreases the number of message transmissions between tags and tag readers. Anti-collision algorithms based on tree structures show reasonable accuracy and cost, but the performance of them can be degraded because the number of message transmissions between tags and readers exponentially increases depending on the size of ID. The proposed algorithm resolves this problem. Accordingly, the performance of proposed algorithm is improved as the length of tag ID is increased.