A first communication device for handling a Packet Data Convergence Protocol, PDCP, operation in a 3GPP wireless communication system , comprising: at least one storage device ; and at least one processing circuit , coupled to the at least one storage device , wherein the at least one storage device stores, and the at least one processing circuit is configured to execute, instructions of: receiving a first plurality of PDCP Data Protocol Data Units, PDUs, associated to a radio bearer, RB, from a second communication device; processing the first plurality of PDCP Data PDUs according to a RX_NEXT, a RX_DELIV and a RX_REORD which are associated to the RB; updating the RX_NEXT, the RX_DELIV and the RX_REORD, when processing the first plurality of PDCP Data PDUs; performing a PDCP reestablishment, after updating the RX_NEXT, the RX_DELIV and the RX_REORD; characterised by : setting the RX_NEXT, the RX_DELIV and the RX_REORD to a plurality of initial values in response to the PDCP reestablishment, wherein the initial values for the RX_NEXT and for the RX_DELIV are 0; receiving a second PDCP Data PDU associated to the RB, from the second communication device, after the PDCP reestablishment; and processing the second PDCP Data PDU according to the RX_NEXT, the RX_DELIV and the RX_REORD, after setting the RX_NEXT, the RX_DELIV and the RX_REORD to the plurality of initial values. at least one storage device ; and at least one processing circuit , coupled to the at least one storage device , wherein the at least one storage device stores, and the at least one processing circuit is configured to execute, instructions of: receiving a first plurality of PDCP Data Protocol Data Units, PDUs, associated to a radio bearer, RB, from a second communication device; processing the first plurality of PDCP Data PDUs according to a RX_NEXT, a RX_DELIV and a RX_REORD which are associated to the RB; updating the RX_NEXT, the RX_DELIV and the RX_REORD, when processing the first plurality of PDCP Data PDUs; performing a PDCP reestablishment, after updating the RX_NEXT, the RX_DELIV and the RX_REORD; receiving a first plurality of PDCP Data Protocol Data Units, PDUs, associated to a radio bearer, RB, from a second communication device; processing the first plurality of PDCP Data PDUs according to a RX_NEXT, a RX_DELIV and a RX_REORD which are associated to the RB; updating the RX_NEXT, the RX_DELIV and the RX_REORD, when processing the first plurality of PDCP Data PDUs; performing a PDCP reestablishment, after updating the RX_NEXT, the RX_DELIV and the RX_REORD; characterised by : setting the RX_NEXT, the RX_DELIV and the RX_REORD to a plurality of initial values in response to the PDCP reestablishment, wherein the initial values for the RX_NEXT and for the RX_DELIV are 0; receiving a second PDCP Data PDU associated to the RB, from the second communication device, after the PDCP reestablishment; and processing the second PDCP Data PDU according to the RX_NEXT, the RX_DELIV and the RX_REORD, after setting the RX_NEXT, the RX_DELIV and the RX_REORD to the plurality of initial values. setting the RX_NEXT, the RX_DELIV and the RX_REORD to a plurality of initial values in response to the PDCP reestablishment, wherein the initial values for the RX_NEXT and for the RX_DELIV are 0; receiving a second PDCP Data PDU associated to the RB, from the second communication device, after the PDCP reestablishment; and processing the second PDCP Data PDU according to the RX_NEXT, the RX_DELIV and the RX_REORD, after setting the RX_NEXT, the RX_DELIV and the RX_REORD to the plurality of initial values. <EOS>