The present invention relates to a packet retransmission method of a terminal accessing a base station in contention-based access mode, and the method includes transmitting an uplink packet to the base station; receiving, when the base station fails decoding the uplink packet, a retransmission request message transmitted by the base station; and initiating, when the retransmission request message is received, a Radio Link Control (RLC) retransmission. According to the present invention, the terminal operating in contention-based access mode initiates RLC retransmission in reception of an HARQ NACK from the base station. Accordingly, it is possible to perform the RLC retransmission immediately without necessity of waiting for the expiry of HARQ RTT as in the HARQ retransmission, resulting in reduction of packet retransmission delay.