The enantioselective hydrolysis of racemic esters and simultaneous separation of the corresponding optically pure (S)-acid as pure isomer is of considerable interest to the pharmaceutical industry as a route to non-steroidal anti-inflammatory drugs. In the present study, an enzymic membrane reactor (EMR) was employed for the optical resolution of racemic ibuprofen ester. EMR consisted of a lipase immobilized polymeric membrane, an organic phase dissolving ester and an aqueous phase to recover the reaction products. The catalytic behaviour of lipase immobilized in a polymeric hollow fibre membrane was investigated using 1-heptyl-ibuprofen ester and 2-ethoxyethyl-ibuprofen ester. The two ester substrates differ in the nature of the alkyl group of the alcohol moiety. The performance of the immobilized enzyme was studied as a function of temperature, pH of phosphate buffer solution and substrate flow rate. The operational conditions that favoured the enzyme selectivity for the (S)-ibuprofen esters, in order to obtain the corresponding (S)-ibuprofen acid as an optically pure single enantiomer, were identified. Lipase from Candida rugosa was used in the hydrolysis of racemic ibuprofen ester. (R)-Ibuprofen ester was found to be less reactive in the reaction. Highest enantioselectivity of enzyme was obtained with phosphate buffer solution of pH 8.0 at temperature of 40 degrees C and at lower substrate flow rate for both racemic 1-heptyl-ibuprofen and 2-ethoxyethyl-ibuprofen esters. The hydrolysis of racentic 1-heptyl-ibuprofen ester gave 4% ee(S), 90% ee(P) and E value of 1-4, while the hydrolysis of 2-ethoxyethyl-ibuprofen ester resulted in 31% ee(S), 85% ee(P) and E value of 9.5-13 by running the experiment under optimum operating condition in an enzymatic membrane reactor. (c) 2004 Elsevier Ltd. All rights reserved.