The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for establishing layer-2 entities for D2D communication system, the method comprising: configuring a sidelink radio bearer over which the UE transmits data to a peer UE; establishing RLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol) entities for the sidelink radio bearer; and transmitting configuration information of the sidelink radio bearer via a sidelink to the peer UE, wherein the UE is directly connected to the peer UE via the sidelink.