An apparatus is capable of allocating an ACK/NACK channel in a wireless communication system. The apparatus performs a method for allocating the ACK/NACK channel at a base station that includes generating ACK/NACK channel allocation information of a packet transmitted to a terminal; inserting the ACK/NACK channel allocation information into the packet using a padding area indicative of a size difference of data carried by the packet and an Automatic Repeat Request (ARQ) block; and transmitting the packet comprising the inserted ACK/NACK channel allocation information to a terminal to service.