Currently, ethanol has gained significance since it is substantially used as an alternative biofuel. It can be produced by agro-industrial residuals such as corncobs. In ethanol production, hemicellulose and lignin are inhibitors of the enzymatic hydrolysis between cellulase and cellulose. They must be removed during in the pretreatment stage. In this research H2SO4 and NaOH were used as pretreatment solution at high temperature. The temperature were varied for 120 to 170 °C. The result showed that the optimal pretreatment condition of corncobs was using 2% (v/v) NaOH for 24 hr digestion in 1% (v/v) H2SO4 and then heating at 170 °C for 5 min. At this condition, the cellulose content of corncobs increased from 66.52% (untreated) to 92.25% (pretreated). Enzyme digestion of pretreated corncobs at an optimum condition yielded the reducing sugar level of 8.74 g/L. The optimum conditions were achieved at cellulase loading of 10 FPU/g and digestion time of 4 hr. Finally, the reducing sugar solution of 5 g/L was fermented with Zymomonas mobilis TISTR405 at 30°C and pH 5.0 for 48 hr, yielding ethanol of 1.8 g/l or 35.93% of the theoretical ethanol yield.