Disclosed herein is a handover method for a mobile communication terminal in a mobile communication network in which an asynchronous network and a synchronous network coexist. In the present invention, as a mobile communication terminal, which is making a call through an asynchronous mobile communication system, moves into the area of a synchronous mobile communication system, and thus a handover event occurs, the establishment of a call with a synchronous mobile communication system is performed by the automatic call termination or origination of the mobile communication terminal while a connection between the asynchronous modem unit of the mobile communication terminal and the asynchronous mobile communication system is maintained, and then the connection with the asynchronous mobile communication system is released. Accordingly, a call interruption can be prevented at the time of handover between heterogeneous networks.