Disclosed are a method and an apparatus for performing a random access by a user equipment in. The method includes transmitting a random access preamble to an evolved-NodeB (eNB) on at least one serving cell; and receiving a random access response message as a response to the random access preamble from the eNB, wherein the random access response message is transmitted through a physical downlink shared channel (PDSCH) ordered by a physical downlink control channel (PDCCH) scrambled by the at least one random access radio network temporary identifier (RA-RNTI) for the at least one serving cell, respectively. The UE can receive timing information for uplink synchronization through a plurality of serving cells to perform the uplink synchronization with the eNB and more effectively configure the random access response message transmitted from the eNB to the UE for uplink synchronization.