In　an　aqueous　buffer　system,　serious　reverse　and　side　reactions　were　found　in　the　asymmetric　reduction　of　2-octanone　with　Saccharomyces　cerevisiae.　However,　some　nonionic　surfactants　added　to　the　aqueous　buffer　system　improved　the　bioreduction　process　by　decreasing　the　reverse　and　side　reaction　rates　in　addition　to　effectively　increasing　the　average　positive　reaction　rate.　Further,　a　shorter　carbon　chain　length　of　hydrophilic　or　hydrophobic　moieties　in　surfactants　resulted　in　a　higher　yield　of　(S)-2-octanol.　The　alkylphenol　ethoxylate　surfactants　had　a　less　influence　than　polyoxyethylenesorbitan　trialiphatic　surfactants　on　the　product　e.e.　It　suggested　that　the　product　e.e.　resulting　from　the　change　of　carbon　chain　length　of　the　hydrophobic　moieties　varied　markedly　compared　with　the　change　of　carbon　chain　length　of　the　hydrophilic　moiety.　Emulsifier　OP-10　and　Tween　20　markedly　enhanced　the　yield　and　product　e.e.　at　the　concentration　of　0.4　mmol　L-1　with　a　yield　of　73.3　and　93.2%,　and　the　product　e.e.　of　99.2　and　99.3%,　respectively,　at　the　reaction　time　of　96　h.