Ethanol was produced by SSF at 37◦C and 130 rpm under anaer-obic conditions for 72 h. A medium containing: yeast extract, 5 (g/l);(NH4)2SO4, 7.5 (g/l); K2HPO4, 3.5 (g/l); MgSO4·7H2O, 0.75 (g/l);CaCl2·2H2O, 1 (g/l); and pretreated or untreated rice straw, 50 (g/l);was prepared in 0.05 M buffer citrate. Medium pH was adjusted to5.5 ± 0.1 by 1 M sodium hydroxide. It was then autoclaved at 121◦Cfor 20 min. After cooling, 1 g/l of prepared microorganisms (basedon the dry weight) together with 20 FPU cellulase and 30 IU -glucosidase per gram of substrate and 2.5 g/l Tween 20 were added.The media was purged with pure nitrogen gas at the beginningof fermentation to ensure obtaining anaerobic conditions (Karimiet al., 2006).