The present invention relates to a method for offloading traffic by means of wireless LAN in a mobile communications system and apparatus therefor, and more particularly to a method for a terminal to offload traffic at a bearer level, and to a base station communicating with the terminal. The method for a terminal to offload traffic according to the present invention includes the steps of: while performing a data communication with a base station through a bearer of a first communications network, receiving from the base station an offloading command for offloading a part of traffic to a second communications network; transmitting a report of the offloading to the base station in response to the offloading command; and performing a data communication of the partial traffic with an accessible AP through a bearer of the second communications network without releasing the bearer of the first communications network.