A method for operating a plurality of carriers by a user equipment in a wireless communication system supporting a primary carrier and at least one secondary carrier, the method includes transmitting, to a base station, carrier capability information; receiving, from the base station, carrier configuration information, the carrier configuration information including an index of the at least one secondary carrier configured for the user equipment, the carrier configuration information being based upon the carrier capability information of the user equipment, the primary carrier being configured as a carrier for performing an initial network entry procedure; receiving, from the base station, a control channel including information regarding multi-carrier operation through the primary carrier; and transmitting, to the base station, traffic through one of the at least one secondary carrier based on the information regarding multi-carrier operation.