A method, performed by a user equipment (UE), of deciphering data in wireless communication system is provided. The method includes receiving a packet data convergence protocol (PDCP) data packet data unit (PDU), determining a RCVD_COUNT of the PDCP data PDU, determining whether integrity protection is performed to the PDCP data PDU, and performing, based on whether the integrity protection is performed to the PDCP data PDU, deciphering of the PDCP data PDU using the RCVD_COUNT, wherein the RCVD_COUNT is determined based on hyper frame number (HFN) of the PDCP data PDU determined according to RCVD_DELIV and sequence number (SN) of the PDCP data PDU, and wherein RX_DELIV is a count value of a first PDCP service data unit (SDU) not delivered to an upper layer of PDCP and waiting to be delivered to the upper layer of PDCP.