A method of informing a terminal of uplink synchronization acquisition in a mobile communication system by using downlink transmit power control (TPC) bits. The base station modifies and transmits power control bit patterns according to certain `N` values defined as a pattern 01 count, and the terminal detects an indicator that informs uplink synchronization acquisition by the modified power control bit pattern. The terminal also maintains the transmit power of the synchronization acquisition timing by increasing the transmit power by an amount equal to the decrease caused by receiving the power control bits for detecting uplink synchronization acquisition.