Improvement of biogas production by pretreatment of rite straw with 0.25 and 0.5 M sodium carbonate at 90, 110, and 130 degrees C and for 1, 2, and 3 h WO investigated, and promising results were obtained. All treated and untreated rice straws were digested under mesophilic conditions (37 degrees C). Increasing the concentration of sodium carbonate showed significant improving effects, whereas the treatment time showed less impact. The best results, obtained by pretreatment with 0.5 M sodium carbonate at 110 degrees C for 2 h, resulted in the production of 292 mL of CH4 per gram of VS; whereas untreated rice straw produced 130 mL of CH4 per gram of VS. Compositional, SEM, and FTIR analyses confirmed that structural modification, lignin removal, and cellulose crystalline reduction are responsible for the improvement.