A bearer reconfiguration method performed by a User Equipment (UE) in a wireless communication system supporting a multi-bearer is provided. The bearer reconfiguration method includes, if the UE performs a bearer reconfiguration from a single bearer to the multi-bearer, reordering Packet Data Convergence Protocol (PDCP) Protocol Data Units (PDUs) received through the multi-bearer, using a timer after a completion of the bearer reconfiguration, and processing the reordered PDCP PDUs into at least one PDCP Service Data Unit (SDU). The method may also include, if the UE performs bearer reconfiguration from the multi-bearer to the single bearer, reordering PDCP PDUs received through the multi-bearer, using a timer until a predetermined condition is satisfied, and processing the reordered PDCP PDUs into at least one PDCP SDU.