A catalytic and stereoselective glycosylation with glucosyl fluoride was effectively performed by using a catalytic amount of various protic acids. When the glycosylation was carried out, for example, using perchloric acid (HClO4) in diethyl ether (Et2O), the major products were alpha -glycosides while beta -stereoselectivity was observed when tetrakis(pentafluorophenyl)boric acid [HB(C6F5)(4)] was used in a mixed solvent of trifluoromethylbenzene (BTF)-pivalonitrile ((BuCN)-Bu-t) = (5:1). The stereoselectivity was controlled by not only the effect of solvent but also by the nature of counter anion of the catalyst such as B(C6F5)(4)(-) or ClO4-.