The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing a cell change procedure in the wireless communication system, the method comprising: receiving configuration information indicating an identifier of a radio bearer to which a cell change procedure be performed; and performing the cell change procedure in RLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol) entities of the radio bearer indicated in the configuration information, wherein the cell change procedure comprises a re-establishment of the RLC and PDCP entities.