Nowadays, progresses of different industries have increased energy consumption. Therefore, increase in green house gases emission, reduction in natural resources, and low availability of fossil fuels intensify the significan ce of using renewable resources. As one of the possible solutions, the importance of bioethanol production as a clean and renewable fuel seems obvious. As a biological process, fermentation of sugar-based, starch-based, and lignocellulosic materials is the dominant method suggested for ethanol production. Lignocellulosic materials are one of the renewable and low cost resources which are abundantly available. Rice straw is an abundant, inexpensive, and widely available lignocellulosic resource which in comparison with other lignocellulosic materials has high silica content. The presence of silica in outer layer of rice straw protects other components and makes difficulty in its composting and processing Silica reduces enzymatic hydrolysis yield of the straw and consequently its ethanol production. In this study, silica removal from rice straw using various chemical substances at different temperatures was investigated. Sodium carbonate at 100 o C was more effective in separation of silica. Moreover, temperature of pretreatment had a pronounced effect on the silica removal. Higher temperatures led to more efficient silica removal. Pretreatment with sodium carbonate at 100 o C removed 91% of silica from rice straw. The untreated and pretreated rice straw with 1 M sodium carbonate at 0, 25, and 100 o C were subjected to enzymatic hydrolysis at 45 o C for 72 h by 20 FPU cellulase and 30 IU ?-glucosidase per each gram of substrate. Pretreatment with sodium carbonate at high temperature caused significant improvement in the glucose production; while the pretreatments at lower temperature had very little influence on the hydrolysis. For optimization of the pretreatment, sodium carbonate solutions were used with concentrations of 0.5 an 1 M, at 100 o C, time intervals of 1, 3 and 7 h, and solid loading of 1 to 10, 15 and 20. The best pretreatment conditions were obtained to be 0.5 M sodium carbonate at 100 °C for 3 h with solid loading of 1 to 20. This pretreatment improved the glucose yield from 35% for the untreated straw to 100% for the treated one. The structural properties of the materials were followed by SEM images and FTIR analysis. The results showed decreasing structural uniformity and crystallinity of cellulose.Ethanol production by simultaneous saccharification and fermentation with M. hiemalis was carried out at 37 o C for 72 h under anaerobic conditions. The results showed that ethanol production yield was improved from 39.8% for untreated straw to 83.2% for treated one at optimum conditions. Moreover, increasing pretreatment times from 1 to 3 h improved the hydrolysis and fermentation, while the increasing in time interval after 3 h had no effect on glucose and ethanol production. In addition, increasing in liquid to solid ratio in pretreatment step, had minor effect on ethanol production. In fact, the ethanol yield of more than 80% can be achieved with using fewer liquid in pretreatment step. To investigate the performance of M. hiemalis in ethanol production, simultaneous saccharification and fermentation was performed with M. hiemalis and S. cerevisiae. The results indicated that the fungus had a better ethanol yield compared to S. cerevisiae. Keywords ethanol, pretreatment, rice straw, silica, sodium carbonate, Mucor hiemalis .