The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for reporting an RLC (Radio Link Control) re-transmission failure in the wireless communication system, the method comprising: communicating with both the first BS and the second BS, wherein the first BS has a Radio Resource Control (RRC) connection with the UE; and reporting to the first BS, a Radio Link Control (RLC) retransmission error without RRC connection re-establishment for the first BS if the RLC retransmission error occurs in an RLC entity transmitting RLC PDU (Protocol Data Unit) to the second BS.