BACKGROUND: Gluconobacter oxydans was applied for enantioselective oxidation of racemic-1,2-propanediol. Accumulation of product in the biotransformation reactor inhibited the activity and enantioselectivity of oxidative enzymes, and it also led to overproduction of lactaidehyde as an intermediate of incomplete oxidation. It was important to improve the enzymatic activity and ee value of the chiral product. RESULTS: The coupling of biotransformation and separation was studied with an in situ product removal method. Anion exchange resin was applied to remove D-lactic acid on line. The ee value achieved was 95% and product yield increased by 50%, compared with the control result without coupling system. CONCLUSION: Coupling of biotransformation and separation effectively decreased the free D-lactic acid concentration in the system. Product inhibition of enzyme activity and enantioselectivity was reduced, and the ee value and product yield were improved. (C) 2009 Society of Chemical Industry