An enzymatic reaction with supercritical carbon dioxide (SCCO2) as the reaction medium was investigated. Lipase could catalyze the batch type reaction of hydrolysis and interesterification (acidolysis) in SCCO2 at 50°C and 29.4 MPa. The time course of interesterification was influenced by the water content as well as by the kind of reaction medium. The initial velocities of hydrolysis and interesterification were greater in SCCO2 than in n-hexane when the water content increased. A part of this difference in reaction velocity was supposed to be due to water, a modifier of the solvent, the solubility of which in SCCO2 was estimated to be a hundred times that in n-hexane.