The present invention provides a method and apparatus for performing hybrid automatic repeat request (HARQ) in a wireless communication system. A terminal transmits a plurality of code words on a physical uplink shared channel (PUSCH) and receives a plurality of acknowledgement/non-acknowledgement (ACK/NACK) signals, which indicates if each of the plurality of code words has been received, on each physical hybrid-ARQ indicator channel (PHICH) corresponding to the respective code words. A downlink resource for which each of the PHICHs is mapped is determined based on the smallest physical resource block (PRB) index (IPRB—RAlowest—index) among PRBs mapped by the PUSCH and on an uplink demodulation reference signal (DMRS) circular shift parameter (nDMRS), and those downlink resources for which PHICHs are mapped respectively do not overlap each other.