A method and apparatus for handling BWP switching based on priority in a wireless communication system is provided. A wireless device receives configuration of multiple bandwidth parts (BWPs) on a cell, wherein the multiple BWPs includes at least one active uplink (UL) BWP for UL transmission and at least one active sidelink (SL) BWP for SL transmission. A wireless device detects a triggering condition for switching to a specific UL BWP which cannot be simultaneously active with the active SL BWP. A wireless device determines whether to switch to the specific UL BWP based on priority information, wherein the priority information includes at least one of UL priority and/or SL priority. A wireless device performs the switching to the specific UL BWP based on the determination.