Provided are a mobile communication system and a cell reselection method of a mobile communication terminal. The mobile communication system includes two or more communication systems using different transmission modes and a mobile communication terminal connectable to the two or more communication systems. The mobile communication terminal measures received signal strength of a satellite communication cell when being switched to an idle mode, divides priority of a satellite communication system using the measured received signal strength and location information of the mobile communication terminal, and sets a first threshold value necessary for cell reselection of the satellite communication system.