Many RFID authentication protocols have been proposed to provide desired security and privacy level for RFID systems. Almost all of these protocols are based symmetric cryptography because of the limited resources of RFID tags. Recently, the researcher have been proposed an RFID security protocol based on chaotic maps. In this paper, the authors analyze the security of this protocol and discover its vulnerabilities. They firstly present a de-synchronization attack in which a passive adversary makes the shared secrets out-of-synchronization by eavesdropping just one protocol session.