A method and apparatus for performing traffic steering from a 3rd generation partnership project (3GPP) access network to a wireless local area network (WLAN) in a wireless communication system is provided. A user equipment (UE) receives radio access network access network (RAN) assistance information for evaluating traffic steering from the 3GPP access network to the WLAN, and attempts to acquire attributes related to the RAN assistance information from a specific WLAN. If at least one of the attributes is not acquired from the specific WLAN, the UE evaluates traffic steering from the 3GPP access network to the WLAN excluding the specific WLAN. The RAN assistance information includes a WLAN signal power threshold and a WLAN load threshold.