The feasibility of preparing L-lactic acid by lipase-catalyzed enantioselective hydrolysis of ethyl lactate in organic solvents was explored.The effects of enzyme sources and organic media on the reaction were examined respectively.The results showed that Candida antarctic lipase B（N435）had both the highest catalytic activity and enantioselectivity.The mixture of tert-butanol and isooctane (1∶1

vol) was the most suitable media for the reaction

and other optimum conditions for catalysis were 200 r8226;min-1 for shaking rate

1∶5 for mass ratio of ethyl lactate to water

0.27 g8226;ml-1 for ethyl lactate concentration

0.8 g8226;mol-1 for enzyme concentration and 60℃ for reaction temperature

respectively.Under these optimal conditions

a product enantiomeric excess (ee) of 90.02% and the yield of 28.69% were achieved after 16 h reaction time.The kinetics of lipase-catalyzed enantioselective hydrolysis of ethyl lactate was investigated too.The experimental results indicated that: the reaction could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both substrates.The effects of D-lactic acid and D-ethyl lactate substrate concentrations on the initial rate of asymmetric hydrolysis were studied.