A random access method of a User Equipment (UE) in a wireless communication system supporting carrier aggregation which allows transmitting data on multiple carriers is provided. A random access method for a wireless communication system supporting carrier aggregation according to the present invention includes receiving, at a terminal, Random Access Channel (RACH) selection information necessary for random access, the RACH selection information being transmitted by a base station; selecting, when the random access is triggered, an uplink carrier on which the random access is attempted based on the RACH selection information; and attempting the random access on the selected uplink carrier.