Provided are apparatus and method of transmitting and receiving a reception acknowledgment signal in a mobile communication system. The apparatus and method of receiving the reception acknowledgment signal includes respectively calculating a probability that the received reception acknowledgment signal is a reception success signal and a probability that the reception acknowledgment signal is a reception failure signal, by using an estimated packet error rate predicted based on a pre-set required packet error rate and determining whether the reception acknowledgment signal is the reception success signal or the reception failure signal. The apparatus and method of transmitting a reception acknowledgment signal includes determining transmission powers of a reception success signal and a reception failure signal in order to maximize a difference between a first complex signal and a second complex signal, the first complex signal being modulated for the reception success and the second complex signal being modulated for the reception failure, based on the average transmission power and a pre-set required packet error rate. The apparatus and method of transmitting reception acknowledgment signals transmits a single packet indicating reception successes or failures for a plurality of received data packets by using variable length coding based on a pre-set required packet error rate. According to the present invention, non-uniformity of frequency between the reception success signal and the reception failure signal is considered to increase correct reception rate of the reception acknowledgment signal.