Lipases are suitable catalysts for the kinetic resolution of racemic mixtures due to their ability to discriminate between enantiomers. For this reason, they have been studied largely to develop reactors for the production of optically pure enantiomers. The main problem in these productive systems is enzyme stability and enantiocatalytic selectivity as a function of time. In this work, the enantiocatalytic properties of lipase as a function of the -OR group length were studied. The methyl, butyl, and octyl esters of naproxen were synthesized and used as reagents. The lipase was used as a free agent and immobilized in a polymeric membrane reactor. The results show that selectivity and stability of the enzyme improved while catalytic activity decreased with the -OR length group. The immobilized enzyme had higher activity compared with the free enzyme. (C) 2007 Elsevier Inc. All rights reserved.