A transmitting/receiving apparatus and method for packet retransmission in a mobile communication system. Upon request for a retransmission from a receiver, a transmitter inverts initially transmitted coded bits if the retransmission is odd-numbered for the same data, modulates the inverted bits, and transmits the modulated bits to the receiver. Then the receiver recovers the coded bits by demodulation. If the coded bits are retransmitted an odd number of times, the receiver decodes the coded bits after inversion. Thus the error probabilities of initial transmission bits and retransmission bits are averaged in effect and decoding performance is improved.