A method and apparatus for triggering radio bearer release by a relay UE in a wireless communication system are disclosed. Preferably, the method includes the relay UE connects with an eNB. The method also includes the relay UE establishes a PDN connection for supporting traffic relaying. The method further includes the relay UE establishes a layer-2 link with a remote UE. In addition, the method includes the relay UE creates a radio bearer between the relay UE and the eNB for forwarding data packets between the remote UE and a PDN corresponding to the PDN connection. Furthermore, the method includes the relay UE sends a NAS message to the eNB if a failure of the layer-2 link is detected. And the method includes the relay UE receives a RRC message indicating release of the radio bearer in response to transmission of the NAS message from the eNB.