A fast uplink data transmission method for a handover is disclosed. This method effectively uses a handover signal when there is data to be transmitted to an uplink during an Intra Radio Access Technology (I-RAT) handover, such that it quickly transmits and receives uplink data. The method of transmitting uplink data in a wireless access system includes, transmitting a message including an information bit to a target base station by a mobile station during a handover, wherein the information bit indicates whether the uplink data is present, and receiving a radio resource for transmitting the uplink data from the target base station, if the information bit indicates the uplink data is present, wherein the radio resource is allocated by the target base station. So, uplink user data can be quickly transmitted to a destination while the UE performs the handover.