Enzymatic esterification reaction of erythritol and oleic acid was carried out in the reaction system of controlled mater content. A higher conversion was obtained when the water content in the system was adjusted ranging from 1,000 to 4,000 ppm. It was shown that the water in such systems was bound to the enzyme protein and needed for appearance of the enzyme activity. The process of crystallization of erythritol appeared to be effective for the acceleration of lipase-catalyzed synthesis.