The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for releasing a sidelink radio bearer for D2D communication system, the method comprising: receiving configuration information including a targetID, a sourceID, and an LCID from a peer UE, wherein the UE receives data from the peer UE over the sidelink radio bearer; configuring a sidelink radio bearer identified by the targetID, the sourceID, and the LCID; establishing a RLC and a PDCP entities for the sidelink radio bearer based on the configuration information received from the peer UE; starting a timer for the sidelink radio bearer; and releasing the sidelink radio bearer when the timer expires.