A method of performing data communication with a base station by a mobile terminal in a wireless communication system includes transmitting uplink data to the base station or receiving downlink data from the base station by using first channel resource assignment information among two or more channel resource assignment information, receiving from the base station a channel resource modification indicator indicating that a channel resource for transmitting or receiving data should be modified, and transmitting the uplink data to the base station or receiving the downlink data from the base station by using second channel resource assignment information among the two or more channel resource assignment information. Therefore, the efficiency of a channel resource can be improved in a wireless communication system.