A method and apparatus for allocating resources for a sidelink transmission in a wireless communication system is provided. A user equipment (UE) selects a first carrier, i.e. anchor carrier, among multiple carriers, and allocates a first resource on the first carrier. The UE allocates a second resource on a second carrier, i.e. non-anchor carrier, based on an offset from the first resource on the first carrier. The UE performs the sidelink transmission by using the first resource on the first carrier and the second resource on the second carrier.