A method of transmitting data in a wireless communication system is provided. The method includes transmitting downlink scheduling information regarding downlink radio resource allocation and uplink scheduling information regarding uplink radio resource allocation on a downlink control channel, transmitting downlink data on a downlink data channel according to the downlink scheduling information, and detecting an acknowledgement (ACK)/negative-acknowledgement (NACK) signal for the downlink data from a radio resource exclusively allocated to the ACK/NACK signal. According to the present invention, when an error occurs in a downlink control channel due to deterioration of a channel condition, the error can be promptly handled using an error detection protocol agreed between a user equipment and a base station. Therefore, data can be transmitted with higher reliability.