A method for handling Packet Data Convergence Protocol, PDCP, operation in a wireless communication system, comprising: receiving, by a E-UTRA-NR Dual Connectivity, EN-DC, capable User Equipment, UE, a handover message from a long term evolution, LTE, node, wherein the handover message comprises an indication indicating a Packet Data Convergence Protocol, PDCP, version change from a LTE PDCP to a New Radio, NR, PDCP; indicating, by the EN-DC capable UE, the indication from a LTE Radio Resource Control, RRC, entity of the UE to a receiver LTE PDCP entity of the UE; re-establishing, by the EN-DC capable UE, a LTE RLC entity based on the indication; receiving, by the receiver LTE PDCP entity of the EN-DC capable UE, LTE PDCP Protocol Data Units, PDUs, from the LTE RLC entity upon re-establishing the LTE RLC entity based on the indication; processing, by the EN-DC capable UE, the LTE PDCP PDUs at the receiver LTE PDCP entity using a LTE format; reestablishing, by the EN-DC capable UE, the receiver LTE PDCP entity of the UE and a transmitter LTE PDCP entity of the UE; re-transmitting, by the EN-DC capable UE, PDCP SDUs by a transmitter NR PDCP entity using a NR format, wherein re-transmitting the PDCP SDUs comprises identifying the PDCP SDUs to be re-transmitted, and wherein the identified PDCP SDUs comprise all PDCP SDUs received prior to the LTE PDCP entity reestablishment starting from the first PDCP SDU for which the successful delivery of the corresponding PDCP Data PDU has not been confirmed by lower layers; and processing, by the EN-DC capable UE, PDCP PDUs received by a receiver NR PDCP entity and PDCP SDUs received by the transmitter NR PDCP entity based on a NR PDCP operation. receiving, by a E-UTRA-NR Dual Connectivity, EN-DC, capable User Equipment, UE, a handover message from a long term evolution, LTE, node, wherein the handover message comprises an indication indicating a Packet Data Convergence Protocol, PDCP, version change from a LTE PDCP to a New Radio, NR, PDCP; indicating, by the EN-DC capable UE, the indication from a LTE Radio Resource Control, RRC, entity of the UE to a receiver LTE PDCP entity of the UE; re-establishing, by the EN-DC capable UE, a LTE RLC entity based on the indication; receiving, by the receiver LTE PDCP entity of the EN-DC capable UE, LTE PDCP Protocol Data Units, PDUs, from the LTE RLC entity upon re-establishing the LTE RLC entity based on the indication; processing, by the EN-DC capable UE, the LTE PDCP PDUs at the receiver LTE PDCP entity using a LTE format; reestablishing, by the EN-DC capable UE, the receiver LTE PDCP entity of the UE and a transmitter LTE PDCP entity of the UE; re-transmitting, by the EN-DC capable UE, PDCP SDUs by a transmitter NR PDCP entity using a NR format, wherein re-transmitting the PDCP SDUs comprises identifying the PDCP SDUs to be re-transmitted, and wherein the identified PDCP SDUs comprise all PDCP SDUs received prior to the LTE PDCP entity reestablishment starting from the first PDCP SDU for which the successful delivery of the corresponding PDCP Data PDU has not been confirmed by lower layers; and processing, by the EN-DC capable UE, PDCP PDUs received by a receiver NR PDCP entity and PDCP SDUs received by the transmitter NR PDCP entity based on a NR PDCP operation.