Ionic liquids (ILs) which can dissolve high concentration of sugars and retain enzyme activity have been reported as good reaction media for the synthesis of sugar esters. However, the activities of lipases in ILs are usually lower than those in conventional organic solvents used for sugar ester synthesis. In this work, therefore, the ultrasound irradiation was used to increase enzyme activity in ILs. In lipase-catalyzed esterifications of glucose with vinyl laurate or lauric acid, enzyme activities were highly enhanced by using supersaturated solution under ultrasound irradiation. Furthermore, the stability of enzyme in ILs was not influenced by ultrasound irradiation. (C) 2008 Elsevier Ltd. All rights reserved.