An Inter-RAT handover method is disclosed. A method for supporting an Inter-RAT handover by an IEEE 802.16m MS includes performing, by the MS, pre-registration in an Inter-RAT target BS using a tunneling, if a channel quality of an Inter-RAT neighbor cell is higher than a pre-registration threshold, and transmitting a handover request message for a handover to the target BS to a serving BS, if a channel quality of the neighbor cell is equal to or higher than a handover threshold during a time duration in a scanning of the neighbor cell and a channel quality of the target BS is equal to or higher than that of the neighbor cell. This handover method reduces a time required for a handover from an IEEE 802.16m network to a Non-802.16m network, provides a seamless service, supports a rapid recovery in case of a radio link failure, and increases handover reliability.