In this paper, we propose a novel method for improving the tag collection performance in active RFID systems by modifying the tag collection algorithm in the ISO/IEC 18000-7 standard. The proposed method enables to reduce the time slot size by reducing the response message size from the tag and to decrease the number of command messages from the reader throughout the tag collection process. This results in reducing the time required for tag collection and the battery consumption on tags by decreasing the total amount of messages. Via the simulation experiments, we evaluated the performance of the tag collection applied with the proposed method, compared with that of the basic tag collection complying with the standard. The simulation results showed that the proposed method could decrease the total amount of messages between the reader and tags dramatically and reduce the average tag collection time by 19.99% and 16.03% when the reader requested the additional data of 50 bytes and 100 bytes from the tags, respectively.