Continuous gas phase reduction of 4-methyl-2-pentanone catalyzed by immobilized commercial ketoreductase was investigated. Non-porous glass beads were employed as immobilization carriers. An optimal water activity was found to be 0.9 in terms of high enantioselective productivity, while the reaction temperature was optimized at 303-313 K. The stability and enantioselectivity of the immobilized enzyme were almost the same as a function of the substrate activities. The kinetic parameters (V-max = 190 [mu mol/min/g-protein], K-m,K- (4-methyl-2-pentanone) = 0.405 [-], K-m, (2-propanol) = 0.140 [-]) were estimated.