A lipase-immobilized membrane reactor was applied for the optical resolution of racemic naproxen, and the effect of various operation conditions on reaction rate and enantio-selectivity was examined. The membrane reactor consisted of an organic phase dissolving naproxen ester, a lipase-immobilized polyamide membrane, and an aqueous phase to recover the reaction products. The lipase immobilized in the membrane reactor showed a stable activity for more than 200 h of continuous operation, while the native lipase in emulsioned stirred tank reactor quickly lost its activity showing an half-life time of about 2 h. When crude lipase was used, the biphasic enzyme membrane reactor gave smaller enantio-selectivity compared to the native lipase in the emulsioned tank reactor, whilst the use of pure lipase gave similar results to the native lipase. This paper discusses that other hydrolases present in the crude enzyme powder caused the decrease of enantio-selectivity. Enantio-selectivity depended on the substrate concentration, amount of enzyme loaded in the membrane and immobilization site. In fact, these parameters affect the organic/aqueous interface that plays an important role in the enhancement of enantio-selectivity,