The asymmetric reduction of 2-octanone to 2-octanol by yeast in aqueous phase was investigated.The reduction product was mainly S-2- octanol.The results indicated that the conversion ratio of 2-octanoe and the enantiomeric excess values of product were both satisfactory for asymmetric reduction.It was shown also that in the catalysis of the ketone reduction the co-substrate was required to regenerate the NAD(P)H.The appropriate condition to the reaction was 30 ℃ and pH 3.0 or pH 7.0. The high concentrations of substrate and product would have some toxicity to the yeast cells and the high concentration of 2-octanol would inhibit the reduction reaction.When too much S-2-octanol existed in the medium

the S-2-octanol would be oxidized to 2-octanone by yeast

which showed that yeast could be a biocatalyst not only for reduction of 2-octanone to S-2-octanol

but also for oxidation of S-2-octanol to 2-octanone.