A method for monitoring a downlink control channel, the method performed by a user equipment (UE) configured with multiple carriers includes determining whether to monitor the downlink control channel within either one UE-specific search space or a plurality of UE-specific search spaces, and monitoring the downlink control channel within the plurality of UE-specific search spaces if carrier index is configured, wherein each of the plurality of the UE-specific search spaces is determined based on the carrier index.