A trapped aqueous-organic biphase system for the continuous production of (S)-(+)-2-(6-methoxy-2-naphthyl) propionic acid (Naproxen) has been developed. The process consists of a stereoselective hydrolysis of the racemic Naproxen methyl ester by Candida rugosa lipase in a trapped aqueous-organic biphase system. The reaction has been carried our in a laboratory-scale continuous-flow stirred tank reactor (CSTR). The staring material has been supplied in and remaining substrate recovered by organic phase. YWG-C6H5, a poorly polar synthetic support, has been employed to immobilize the lipase and to restrict the aqueous phase. Lipase immobilized on YWG-C6H5 containing aqueous phase has been added into the CSTR to catalyze the hydrolysis. A dialysis membrane tube containing a continuous flow closed-loop buffer has been applied in the CSTR for the extraction of product and recruiting of the aqueous part consumed. Various reaction conditions have been studied. The activity of immobilized enzyme was effected by the polarity of support, the substrate concentration, logP value of organic phase and the product inhibition. At steady-state operating conditions, an initial conversion of 35% has been obtained. The CSTR was allowed to operate continuously for 60 days at 30 degrees C with a 30% loss of activity. The hydrolysis reaction yielded (S)-(+)-Naproxen with >90% enantiomeric excess and overall conversion of 30%. (C) 2000 John Wiley & Sons, Inc.