Catalytic and stereoselective glycosylation with glycosyl fluoride using carbocationic species paired with tetrakis(pentafluorophenyl)borate [B(C6F5)(4)(-)] Or trifluoromethanesulfonate (TfO-) is investigated. When the glycosylation is carried out using the former catalyst in dichloromethane containing (BuCN)-Bu-t, the major product is beta -glycoside while alpha -selectivity is observed when the latter catalyst in dichloromethane containing Et2O is used. In addition to the characteristic properties of the solvent, the nature of the counter anion such as B(C6F5)(4)(-) or TfO- plays important roles in controlling the selectivity. Thus, an appropriate combination of catalyst and solvent leads to the formation of disaccharides.