R-(-)-mandelic　acid　is　an　important　multifunctional　pharmaceutical　intermediate　in　the　preparation　of　chiral　drugs.　An　sp.　strain　by　l　from　18　strains　of　Saccharomyces　cerevisiae,　Lactoballius,　Streptococcus　faecalis　and　Candida　albicans　had　been　screened　for　transforming　phenylglyoxilic　acid　to　R-(-)-mandelic　acid.　In　this　article,　to　further　study　the　asymmetric　bioreduction　of　phenylglyoxylic　acid　to　mandelic　acid　by　Saccharomyces　cerevisiae　sp.　strain　by1,　the　effect　of　biochemical　factors　on　the　conversion　efficiency　of　substrate　phenylglyoxylic　acid　and　enantiomeric　excess　of　product　R-mandelic　acid　was　investigated　in　detail.　For　some　conditions　tested　in　our　experiments,　the　sp.　strain　by1　showed　very　high　enantioselectivity　toward　the　bioreduction　of　the　substrates.　The　enantiomeric　excess　value　of　desired　product　R-(-)-mandelic　acid　reached　up　to　94.0%.　Whereas,　the　conversion　of　substrate　and　the　yield　of　product　mandelic　acid　were　influenced　evidently　by　the　environmental　factors.　The　substrate　conversion　and　the　yield　of　product　decreased　sharply　with　the　increase　of　initial　substrate　concentration　up　to　20　mmol/L.　The　high　concentration　of　substrates　inhibits　strongly　the　activity　of　redoxase　of　yeast　cells.　Under　the　optimal　conditions:　pH　6.5,　32°C,　initial　concentration　15　mmol/L,　absolute　anaerobic　cultivation　28　h,　the　substrate　conversion　rate　of　97.0%　and　yield　of　product　mandelic　acid　of　96.1%　and　enantiomeric　excess　value　of　R-(-)-mandelic　acid　of　95.1%　could　be　obtained.　This　research　paces　the　way　for　economic　preparation　of　chiral　R-(-)-mandelic　acid.