Disclosed are a method for selecting an access network in a wireless communications system and an apparatus therefor. In a wireless communications system, a method for a terminal to select an access network according to an embodiment of the present invention includes the steps of: receiving the policy information of a first network; receiving the policy information of a second network; determining the load value of a WLAN (Wireless Local Area Network) access network; and comparing the load value with a predetermined reference value so as to determine whether the WLAN access network is overloaded. The predetermined value can be determined by comparing first reference information for determination of the WLAN access network overload contained in the policy information of the first network with second reference information for determination of the WLAN access network overload contained in the policy information of the second network.