This research work was carried out in the biogas laboratory of the Agricultural Engineering Department, Faculty of Agriculture, Mansoura University. The main objectives were to utilize biogas as a fuel for operating a modified kerosene engine that was used to drive an electric generator. The modification constituted the design of a mixing chamber connected to the intake manifold of the engine. The performance and efficiency of the engine were studied under all possible operating conditions using togas fuel with six different nozzle diameters (4, 5, 6, 7, 8, and 9 mm) and generator electric loads (0, 0.29, 0.58, 0.87, 1.16, 1.43, and 1.62 kW). It was compared with an engine operating on kerosene fuel only. The obtained results showed that the biogas can be used as a new fuel for operating the modified engine-generator unit at the rated and maximum output of generator (1.43 and 1.62 kW, respectively) using nozzle diameter of 5 mm under biogas pressure ranging from 19 to 21 mbar. Under these conditions, high brake thermal efficiency and mechanical efficiency of the engine and high generator thermal efficiency and electric generation efficiency were 28.03, 80.33 and 81.93%, respectively. The obtained data also revealed that, using nozzle diameter of 5 mm, resulted in reduction in the biogas consumption and specific biogas consumption rate.