This paper describes the system concept of a millimeter-wave personal satellite communication, which includes the configuration of the communication system, the satellite system, and the earth terminal system. The system has a large channel capacity and achieves high performance through a flexible channel set-up method, efficient frequency reuse, and onboard communication equipment such as a baseband channel switching processor and a modulator and demodulator (Modem). Two examples of communication systems are shown, in which the information bit rate, the number of multi-beams, and the antenna diameters are different. On the assumption that a 2 ton class satellite will be used, rough estimates are made of the size, weight, and power consumption of the onboard communication system and bus system of the satellite