Optically active 1-phenyl-1,2-ethanediol is an extremely valuable and versatile alcohol used as a chiral building block in organic synthesis. Among the microorganisms which are able to produce S-1-phenyl-1,2-ethanediol from the racemate by asymmetric conversion, Candida parapsilosis SYB-1 was selected as an candidate biocatalyst for the preparation of S-1-phenyl-1,2-ethanediol with the optical purity of 91% e.e. and the yield of 88%. It is found that the optimal conditions for biocatalytic conversion were 5% cells, 8?R,S-1-phenyl-1,2-ethanediol, pH 6.5, temperature 33oC and reaction time 48 h. Under such conditions, the optical purity of S-1-phenyl-1,2-ethanediol was improved from 91% e.e. to 99% e.e. By detecting the intermediate produced in the reaction by GC-MS, it was suggested that S-enantiomer was produced from the intermediate identified as b-hydroxyacetophenone by asymmetric reduction after stereoselective oxidation of R-enantiomer to b-hydroxyacetophenone.