The　kinetic　characteristics　of　the　reduction　of　phenylglyoxylic　acid　(PGA)　to　R-(-)-mandelic　acid　(R-MA)　by　the　immobilized　yeast　Saccharomyces　cerevisiae　FD11b　were　studied.　Compared　with　the　free　cells,　the　immobilized　cells　showed　a　higher　enantioselectivity　for　the　production　of　R-MA.　However　the　specific　production　rate　(qp)　of　R-MA　with　the　immobilized　cells　was　lower　than　that　with　free　cells　due　to　the　effects　of　the　external　and　internal　diffusion.　When　the　agitation　rate　was　above　200　rpm,　the　effect　of　the　external　diffusion　could　be　eliminated.　The　effects　of　the　granule　diameter　and　the　cell　density　immobilized　in　the　granules　on　the　internal　diffusion　rate　of　the　substrate　and　the　specific　production　rate　of　R-MA　(qp)　were　investigated.　A　mathematical　model　considering　the　internal　diffusion　and　reduction　kinetics　was　developed　to　analyze　the　effect　of　the　internal　mass　transfer.　The　experimental　data　and　the　simulative　results　showed　that　the　effect　of　the　internal　diffusion　on　qp　could　be　eliminated　when　the　granule　diameter　was　less　than　2.2　mm　and　the　cell　density　immobilized　was　lower　than　66.7　gdw/L-granules.　After　excluding　the　effect　of　the　external　and　internal　diffusion,　qp　reached　0.355　mmol　gdw-1　h-1,　close　to　that　with　free　cells　(0.360　mmol　gdw-1　h-1)　in　the　same　reaction　system.　The　optimal　pH　for　the　reduction　of　PGA　with　immobilized　FD11b　was　7.5,　and　the　optimal　temperature　was　32　°C.　©　2007.