T The occurrence of energy crisis in recent years has caused much economical problems to many countries. Many scientist and engineers have been trying to investigate and develop alternative sources of energy, from which biogas process generating methane from anaerobic decomposition of organic waste is identified. Biogas is a by-product of anaerobic fermentation of organic matters, which consist of 54-70% methane and 27-45% carbon dioxide. In this experiment, the raw material used is the mixture of rice straw and cows dung in several compositions. So we can determine the proper composition of rice straw and cow dung for the anaerobic bacteria to digest the organic matters, hence yielding maximum methane production.The experiment consists of three units. Unit I for 1:9 ratio, Unit II for 3:17 ratio and Unit III for 3:17 ratio. Total weight of each unit is 200 gr. Total experiments held for each unit are three times in order to obtain the data validity. And as the control, 0:1 ratio is used.As the result, unit III was found to be the best unit. If we compare to the other unit, the gas production curve is more stable and short. Total production time is 15 days with an average gas production is 25.27 ml/days. Volatile solid content is 67.4b %. Biogas composition for Unit III shows the best composition, which has the highest methane contents (58.38 % methane and 41.62 % Carbon dioxide). As for control, total production time is 20 days with an average gas production 20.75 ml/days. Volatile solid content for Control is 75.82 %. Biogas composition consist of 30.18 % methane and 68.82 % carbon dioxide.After the experiments, the conclusions are the addition of rice straw in cow dung fermentation can make the total production time shorter, raise the average gas production and the methane content.