Abstract: There are two challenges for the frame-slotted ALOHA algorithms in radio-frequency identification (RFID). The first challenge is estimating unknown tag-set size accurately; the second challenge is improving the efficiency of the arbitration process so that it uses less time slots to read all tags. A novel anti-collision technique is proposed to maximize identification performance in slotted ALOHA based RFID systems. The performances of these protocols are evaluated and it is verified that this protocols outperforms the traditional frame slotted ALOHA protocols.