Methods and apparatuses for transmitting and receiving at least one Downlink Control Information (DCI) in a communication system supporting Carrier Aggregation (CA) are provided. The method for receiving includes receiving information representative of presence of carrier indicator by higher layer signaling from a Node B; receiving information representative of at least one cell indicator by higher layer signaling from the Node B; defining an UE specific search space based on aggregation level, an UE ID, and at least one carrier indicator value, where the UE specific search space includes a set of Physical Downlink Control CHannel (PDCCH) candidates based on the aggregation level; decoding at least one PDCCH including at least one DCI respectively by the UE ID; and acquiring the at least one DCI, wherein the at least one carrier indicator value is based on the at least one cell indicator.