The limited resources of oil and the increase in population is one of the problems in the world, it is that drives us to do development and research on the alternative fuel. Biogas is a fuel derived from palm oil waste, and manure can be used as an alternative fuel for diesel engines. In this study, the biogas is used as a fuel in a diesel engine generator set stationary single-cylinder modified with dual fuel system (dual fuel) to generate electricity. To determine the effect of the performance of the machine, we variasikannya with biogas fuel flow rate. Performance is calculated is the power, torque, thermal efficiency, fuel consumption (SFC) and the ratio of air to fuel (AFR) with test machines using a static load of 600, 900, 1200 and 1500 Watt, as well as engine speed is increased slowly from 1000 up to 1500 RPM, and the addition of a catalytic converter in the hope of reducing exhaust emissions. Then the performance test results were compared with the same diesel engine generator set, using pure diesel fuel, so that it can be seen the influence of biogas for diesel engine performance. And also testing exhaust emissions to meet the eligibility standardization of engines that use diesel fuel and biogas. Also the economic value ratio calculation to determine the efficiency of the economic value of the fuel changes. From the test results showed that, the power and torque of the engine tends to increase for several biogas stream flow rate, increased thermal efficiency for the entire biogas flow rate decreases while the SFC and the AFR for the entire biogas flow rate. By using biogas, can reduce the consumption of diesel fuel (diesel economic value). 100401075