A transmit phase control system of synchronization burst is disclosed for use in a SDMA/TDMA satellite communication system in which a phase error between a synchronization burst transmitted from an earth station and a synchronization window, assigned as a time slot on a satellite for returning the synchronization burst, is measured and the transmit phase of the synchronization burst is controlled based on the measured value. Phase error measurement is achieved a plurality of times in connection with the received synchronization burst of each station, and a decided phase error is derived based on the measured value obtained by the plurality of measurements. The transmit phase of the synchronization burst is then controlled in accordance with the decided phase error. Further, the phase error decision is achieved at every 1/n (n being an integer larger than 1) round trip and the present synchronization burst is transmitted with its transmit phase corrected corresponding to a value that is the sum of the phase corrected value of the n preceding phase correction instants subtracted from the decided phase error at the present instant.