Abstract: Effluent from anaerobic digestion was used in this experiment to ret rice straws.An orthogonal experiment program was carried out to determine effects of temperature,moisture,time and MLSS(mixed liquid suspended solid) on biogas generation during anaerobic digestion and compare retted rice straws with un-retted ones in biogas generation under different loadings of organic substances.Results show that the total biogas yield of retted rice straws was about 3%-49.5% higher than the untreated one.The optimal conditions for biogas generation were 30 ℃ in temperature,900 g·kg^-1 in moisture,10 days in time and MLSS at 1 500 mg·L^-1 in volume.Under such conditions,the biogas yield of retted rice straws reached 804.8 mL·g-1 VS(volatile solid),51.2% higher than that of untreated ones and the yield peaked 10 days earlier.