A method for transmitting ACK/NACK signal in a wireless communication system applied carrier aggregation is disclosed herein. More specifically, the method includes receiving multiple transmission blocks respectively through multiple downlink component carriers from a base station, determining ACK/NACK responses corresponding to each of the multiple transmission blocks by decoding the multiple transmission blocks, mapping the ACK/NACK responses to a ACK/NACK state information, and transmitting the ACK/NACK state information through a single uplink component carrier, wherein ACK information included in the ACK/NACK state information indicates a number of ACK response among the ACK/NACK responses.