One of the most important ways that conserve fossil fuels is the use of renewable resources. Biogas is one of the most important renewable resources. Biogas is created from anaerobic fermentation of livestock waste in a fermentation chamber. Biogas technology is an important from several aspects First, the significant social impact of this technology in the field of environment and human health. Second, it can be fired using biogas generators for generate electricity and third, sludge biogas unit output, would be a rich fertilizer that can greatly increase the efficiency of agricultural products. This paper delivers a cost-benefit analysis of biogas-fired plants, from the perspective of the private sector and the public sector, of the dairy industry in Iran. The results of both analyzes indicate high economic efficiency in the different sizes of biogas-fired power plants in Iran dairy industry.