A method for selecting an access network in a terminal of a mobile communication system according to one embodiment of the present specification comprises the steps of: if traffic is generated in the terminal, selecting an access network according to the characteristics of the generated traffic and network selection policy information; and transmitting and receiving the generated traffic via the selected access network. According to the embodiment, the present invention adjusts priorities of accesses given to users and applications in a wireless communication system including heterogenerous networks, thereby reducing processes for reselecting an access network of a user terminal, and reducing the cases of unnecessarily accessing a network having a low priority or requiring high costs for a long time. Therefore, the present invention can enhance user convenience and improve communication efficiency.