A method of performing hybrid automatic repeat request (HARQ) performed by a user equipment (UE) in a wireless communication system is provided. The method includes receiving downlink assignments in a first subframe, a downlink assignment being transmitted based on a control channel element (CCE), the CCE being a logically indexed resource unit, receiving downlink data on a downlink shared channel in the first subframe, the downlink shared channel being assigned according to the downlink assignments, generating ACK/NACK signals which indicate successful or unsuccessful reception of the downlink data, and transmitting in a second subframe, the ACK/NACK signals by using uplink resources of a subset, the subset being mapped to the first subframe, at least one of the uplink resources being mapped to a plurality of CCEs in the first subframe. Limited resources for uplink feedback are effectively used to support HARQ operation.