In the handover method, a radio network controller periodically measures the wireless environment of a mobile communication terminal, determines whether handover is required, and informs the asynchronous mobile switching center of the asynchronous communication system that the handover is required. The asynchronous mobile switching center requests the handover and a synchronous mobile switching center assigns a forward channel to the mobile communication terminal. The mobile communication terminal prepares for communication with a synchronous mobile communication system according to the direction of the asynchronous mobile switching center, and causes a backward channel with respect to the synchronous communication system to be assigned to the mobile communication terminal. The synchronous mobile switching center informs the asynchronous mobile switching center that handover has been completed, and causes a connection between the asynchronous mobile switching center and the radio network controller to be released.