An　efficient　method　is　reported　for　the　copper(I)-catalyzed　trifluoromethylthiolation　of　allylic　bromides　by　using　elemental　sulfur　and　CF3SiMe3.　This　rate　of　this　transformation　was　significantly　accelerated　in　the　presence　of　18-crown-6,　and　the　reaction　afforded　the　desired　products　in　moderate　to　excellent　yields　with　high　stereo-　and　regioselectivity.　This　method　can　tolerate　a　number　of　functional　groups　and　provides　facile　access　to　a　variety　of　allylic　trifluoromethyl　thioethers.　The　copper(I)-catalyzed　trifluoromethylthiolation　of　propargylic　chlorides　was　also　investigated.　A　plausible　mechanism　that　involves　an　allylcopper(III)　intermediate　is　proposed.