Abstract: Disclosed herein is a method and system for Mobile Internet Protocol version 4 (MIPv4)-based fast handoff between heterogeneous networks. The method includes the first step of an Mobile Station (MS) acquiring information about a second Foreign Agent (FA) pertaining to a second wireless network to be newly accessed from a first FA pertaining to a first wireless network that is different from the first wireless network and is previously accessed; the second step of the MS requesting registration from an integrated Home Agent (HA) through the first FA and the second FA; the third step of generating a temporary tunnel between the first FA and the second FA; and the fourth step of the HA transmitting a reply to the registration request to the MS through the second FA.