The heterogeneous mobile network proposed to provide a high data transmission and high mobility under wide area coverage is a candidate to integrate all kinds of communication networks in the future mobile communications. In this paper, a novel re-authentication protocol named Fast Iterative Localized Re-authentication (FIL Re-authentication) is proposed to replace the fast reauthentication protocol in EAP-SIM and it adopts localized process and iterative process within the access points (APs) for reducing the authentication latency. Additionally, the IEEE 802.11 WLAN simulation mode based on the Network Simulator 2 (NS-2) is used for validating the proposed protocol and for analyzing the performances of the proposed protocol shown superior results in comparison to existing EAP-SIM protocol in terms of authentication session time, bandwidth cost, and authentication delay¹.