A method for configuring an acknowledgement for a hybrid automatic repeat request (HARQ) in a wireless communication system. The method includes receiving downlink data through one of a first downlink component carrier and a second downlink component carrier from a base station; and determining whether the first or second downlink component carrier is used for receiving the downlink data. If the first downlink component carrier is used for receiving the downlink data, the resource used for the PUCCH is determined by using a control channel element (CCE). If the second downlink component carrier is used for receiving the downlink data, the resource used for the PUCCH is determined by using a radio resource control (RRC) message. The resource used for the PUCCH is associated with an orthogonal sequence with which the ACK/NACK signal is spread.