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The purpose of the present study was to investigate the optimum condition for ethanol production from acid-hydrolyzed cassava starch by a thermotolerant yeast Saccharomyces cerevisiae RMU Y-10 using L9 (34) an Orthogonal array design. Three parameters: pH (4, 5 and 6), magnesium sulphate (0.25 0.50 and 0.75 g/l) and di-ammonium phosphate (0.25, 0.50 and 0.75 g/l) were optimized, all batch fermentations were carried out at 40˚C. The ethanol concentrations from YM medium, pretreated cassava without and with YM medium were used as experiment 1, 2 and 3, respectively. The results revealed that the order of these parameters influences on ethanol concentration was pH > di-ammonium phosphate > magnesium sulphate, respectively. The optimal condition for ethanol production was pH 5, magnesium sulphate 0.50 g/l and di-ammonium phosphate 0.75 g/l. The highest concentration of ethanol (58.21 g/l) was obtained at 36 h of fermentation time, while the ethanol yield and productivity were 0.46 and 1.61 g/l/h, respectively. The results also showed the ethanol concentration and productivity under the optimal condition which were higher than those of the control experiments.