The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for handling for Bandwidth Part operation in wireless communication system, the method comprising: starting a timer related to a downlink (DL) bandwidth part (BWP), when an active BWP for a serving cell is switched to the DL BWP; wherein DL semi-persistent scheduling (SPS) resources are configured on the DL BWP and uplink (UL) SPS resources are configured on a UL BWP related with the DL BWP; transmitting UL data on one of the UL SPS resources or receiving DL data on one of the DL SPS resources; and restarting the timer related to the DL BWP when the UL data is transmitted on the UL SPS resource or the DL data is received in the DL SPS resource.