Environmentally benign and stereoselective beta-glycosidations of glycopyranosyl phosphites and alcohols using a reusable heterogeneous solid acid, montmorillonite K-10, as an activator have been developed. By these glycosidations, beta-gluco-, 2-deoxy-betagluco-, and beta-mannopyrano sides were selectively produced in good to high yields. (C) 2004 Elsevier Ltd. All rights reserved.