Abstract: A handoff method and apparatus between a mobile communication network and a WLAN are provided. A router routes data traffic from an Internet network to a terminal to a first node of the mobile communication network. The first node determines whether any call set up exists for a data traffic received from the router to the mobile communication network, and according thereto, routes the data traffic to a second node of the mobile communication network or an access router or the WLAN. The access router, connected to the router and the first node, transmits the data traffic from the first node to the terminal and transmits the data traffic from the terminal to the router. The second node exchanges the data traffics received from the first node with the terminal located in the mobile communication network. A DHCP server supports the terminal such that the terminal can use an IP address previously allocated before handoff even after the handoff.