In an automatic time setting method of an asynchronous mobile communication terminal, when a user moves from a first area to a second area in a GSM/GPRS network, a time difference between the two areas is calculated by using LAIs or RAIs of the first and second areas, and a time of the terminal is reset according to the calculated time difference. The asynchronous mobile communication terminal includes a RTC (real time clock) circuit for generating time information; a memory for storing time difference information between areas; and a CPU for reading a time difference corresponding to area information of a first and a second areas from the memory when a user moves from the first area to the second area and controlling the RTC circuit.