A method and apparatus for routing traffic in a wireless communication system is provided. A user equipment (UE) transmits information on the routing of the traffic to a network, and routes the traffic to at least one of 3rd generation partnership protocol (3GPP) long-term evolution (LTE) or wireless local area network (WLAN), according to the information on routing of the traffic. The information on the routing of the traffic may be a ratio of an amount of the traffic to be served by the 3GPP LTE and an amount of the traffic to be served by the WLAN, or a preferred WLAN throughput.