Three kinds of SO3H-functionalized Bronsted-acidic ionic liquids with different acidities were applied to the etherification of glycerol with tert-butyl alcohol. High conversion and good selectivity were obtained under mild conditions. Among the ionic liquids investigated, those having a HSO4- anion afforded the highest glycerol conversion and those having a F3CSO3- anion afforded the largest head product selectivity for glycerol etherification. The minimum-energy geometries and experimental results show that acidities and catalytic activities of ionic liquids are not only related to their structures but also to their immiscibility. (C) 2011 Elsevier B.V. All rights reserved.