Esterification of oleic acid with n-butanol in the presence of Lipozyme(R) was carried out at 25 degrees C in isooctane with various initial water activities. Initial reaction rate as well as equilibrium conversion decreased at high initial water activity, Therefore, removal of water present in the reaction mixtures was essential. A pervaporation process was applied to the lipase-catalyzed synthesis of n-butyl oleate to remove water. Pervaporation selectively separated water from the reaction mixture using a nonporous polymeric membrane, cellulose acetate. Therefore, pervaporation is potentially applicable to remove the water produced from various enzymatic processes, such as synthesis of various esters, peptides, and glycosides in a solvent system as well as in a solvent-free system. (C) 1995 John Wiley and Sons, Inc.