Provided is a method for transmitting an acknowledgment through a base station in a multi-carrier system. The method for transmitting the acknowledgment through the base station in the multi-carrier system comprises the steps of receiving a plurality of uplink transmission blocks through at least one uplink carrier; determining a downlink channel for transmitting a plurality of ACK/NACK signals corresponding to the transmission blocks on the basis of the at least one uplink carrier; and transmitting the ACK/NACK signals on the determined downlink channel.