A novel and efficient glycosyl donor having a p-trifluoromethylbenzylthio-p-trifluoroniethylphenyl formimidate function as a leaving group is easily prepared by the addition of anomeric hydroxyl group of 2,3,4,6-tetra-O-benzoyl-alpha,beta-D-glucopyranose to p-trifluoromethylphenyl isothiocyanate, followed by treatment with p-trifiuoromethylbenzyl bromide. Catalytic and stereoselective glycosylation using this glycosyl donor effectively proceeds by activating its nitorogen atom with various protic and Lewis acids.