To mitigate environmental impacts caused by illegal burning of rice straw in rural fields, anaerobic digestion of rice straw could be an excellent alternative for the treatment of this sub-product of paddy rice harvest. The effect of inoculum/substrate ratio (I/S) on biogas yield and biodegradation of rice straw was carried out in batch reactor under room temperature (25° to 27 °C) and for 60 days of digestion. Results demonstrate a high biogas production (410 L/kgVS) at 0.8 of I/S ratio, with methane content over 70%. The modified Gompertz model was utilized to simulate the cumulative biogas yield from different I/S ratios. Degradation of volatile solids (VS), cellulose, hemicellulose, lignin, silica and cellular content indicated that rumen content is an efficient degrader for lignocellulosic material. This study provides useful parameters to evaluate the biogas production via anaerobic digestion of rice straw, as a promising alternative energy in rural areas.