Disclosed is a multi-mode multi-band mobile communication terminal and a mode switching method thereof wherein a mode switching can be performed between an asynchronous network and a synchronous network by minimizing interruption in communication. According to the switching method of a multi-mode multi-band mobile communication terminal, the power of a signal received from an asynchronous network or a synchronous network is measured and the measured power of the received signal drives a modem portion, thereby switching the mode of the mobile communication terminal.