A highly stereoselective 1,2-cis-alpha-glucosylation reaction was developed, in which the use of a strongly electron-donating tert-butyldimethylsilyl protecting group on the C-2 hydroxy group of a glycosyl donor enhanced the alpha-favoured transition state, and thus resulted in high yield and alpha-selectivity. Synthetic utility of this alpha-glucosylation was demonstrated by the generation of a triglucoside moiety in high-mannose-type oligosaccharides.