The present invention relates to a method by which a terminal transmits/receives data to/from a first base station supporting a first radio access technology and a second base station supporting a second radio access technology in a wireless access system supporting multi-radio access technology (multi-RAT), the method comprising the steps of: executing an initial network entry to the first base station; executing a multi-RAT capability negotiation with the first base station to exchange information needed to access the second base station; a step for executing a scanning on at least one second base station included in the coverage of the first base station, on the basis of the information received from the first base station through the multi-RAT capability negotiation step; executing an access to one second base station of said at least one second base station; and simultaneously transmitting/receiving data to/from the first base station and the second base station accessed through the access step, wherein the step of executing a scanning comprises a step of receiving from the first base station a multi-RAT scan command message for commanding the scanning of said at least one second base station, and a step of executing a scanning of said at least one second base station.