A method for performing handover in a wireless communication system and a device therefor are disclosed. Specifically, the method for performing handover by a user equipment (UE) without a wireless local area network (WLAN) termination (WT) change from a source eNodeB (eNB) to a target eNodeB (eNB) in a wireless communication system, the method includes transmitting an end-marker request for requesting retransmission of an end-marker packet to the target eNB when a loss of the end-marker packet is detected after the handover without the WT change is started, and retransmitting the end-marker request or performing a recovery procedure for the end-marker packet when the end-marker packet is not received from the target eNB after the transmitting the end-marker request.