Methods and apparatuses for an UE operation upon RLF detection in a SL CA in a wireless communication system. A method of operating a UE includes receiving, from a base station (BS), configuration information about multiple sidelink (SL) carriers for a SL carrier aggregation (CA) operation; when a hybrid automatic repeat request (HARQ) feedback corresponding to s SL carrier among the multiple SL carriers is not received for consecutive N times and the SL carrier is not a last configured SL carrier, releasing the SL carrier for a corresponding destination layer 2 identifier (L2 ID); and when the HARQ feedback corresponding to the SL carrier among the multiple SL carriers is not received for a consecutive M times and the SL carrier is the last configured SL carrier, releasing a PC5-radio resource control (PC5-RRC) connection for the corresponding destination L2 ID.