A transmission power control method in a communication system including a base station and a user terminal which performs transmission power control in packet-based radio access includes the steps of transmitting, by the user terminal, a packet; evaluating, by the base station, whether interference caused by the packet is above a predetermined threshold, if the packet is transmitted from another cell; generating, by the base station, transmission power control information for controlling transmission power of the user terminal based on the evaluation result of the interference and transmitting the transmission power control information to the user terminal; and determining, by the user terminal, whether the user terminal controls transmission power based on the transmission power control information, upon transmitting a retransmission packet corresponding to the packet.