A method for performing handover to reduce an interruption time is disclosed. A method for performing handover using a variable uplink grant time comprises transmitting a handover request message to a base station, receiving a handover response message from the base station, the handover response message including an uplink grant time, and receiving an uplink grant from the base station if the uplink grant time comes, and transmitting a handover indication message to the base station. Thus, an unnecessary interruption time during hard handover can be reduced by efficiently improving use of an action time, and an action suitable for a frame structure of the IEEE 802.16m can be performed.