Saccharomyces cerevisiae was known to ferment glucose into ethanol, but S.cerevisiae could not ferment starch into ethanol. This research was to studyethanol fermentation from sweet potato by mix cultures of Rhizopus oryzae and S. cerevisiae. The medium was prepared 10, 15 and 20%(b/v) sweet potato in aquadest into jam’s bottle. The media (50 mL) was inoculated with 1 mL S. cerevisiae 1x106 cfu/mL. After covered by Whatman paper No.41, the bottle added with another 50 mL medium and inoculated with 1 mL R. oryzae 1x105 cfu/mL. Concentration of reducing of sugar, starch, ethanol and biomass was measured everyday. The result showed that 10% sweet potato medium produced the highest content of ethanol that was an amount 2.647% followed by 15% sweet potato medium was 2.623% and 20% sweet potato medium was 2.163%. The optimum fermentation duration to produce the highest content of ethanol was 5 days.