A method and apparatus are disclosed for performing a RA procedure for at least a first D2D communication session and a second D2D communication session in a wireless communication system. The method includes a UE transmitting a first message to a network, wherein the first message is a preamble. The method also includes the UE receiving a second message from the network after transmission of the first message, wherein the second message contains a first UL resource. The method further includes the UE using the first UL resource to transmit a third message to the network after reception of the second message, wherein the third message includes at least a BSR MAC CE. In addition, the method includes the UE determining that the RA procedure is successful if the UE receives a fourth message, wherein the fourth message contains either a second UL resource or at least a D2D resource depending on whether or not the BSR MAC CE is associated with the first D2D communication session and the second D2D communication session.