Synthesis of optically active organosilyl alcohol via asymmetric reduction of prochiral acyl silane with immobilized Saccharomyces cerevisiae type II (a mutant from S. cerevisiae by UV irradiation treatment, named UVSC II) cells compared to free UVSC II cells was studied. It has been found that higher yield and enantiomeric excess (e.e.) of the product could be achieved with immobilized UVSC II cells. To further enhance the product yield and the product e.e., an aqueous/organic biphasic system was used as the reaction medium. The influence of various factors, such as shake speed, organic solvent, volume ratio of water phase to organic phase, buffer pH of water phase, reaction temperature and substrate concentration, was systematically studied and the reaction conditions were optimized with respect to the initial reaction rate, the product yield and the product e.e. All the above-mentioned factors had effect on the reaction to some extent. n-Hexane was found to be the best organic solvent. The optimum shake speed, volume ratio of water phase to organic phase, buffer pH, reaction temperature and substrate concentration were 150 rpm, 1/2, 8.0, 30degreesC and 42 mM, respectively, under which the product yield and the product e.e. were as high as 97.4 and 95.4%. (C) 2004 Elsevier Inc. All rights reserved.