With the increase of energy needs and environmental pollution, alcohol-based alternative fuels are used in spark-ignited (SI) engines. Fusel oil, which is a by-product obtained through distillation of ethanol, contains some valuable alcohols. As alcohols are high-octane, they have an important place among the alternative fuels. Fusel also takes its place among those alternatives as it is high-octane and low on exhaust emissions. In this research, the effects of using blends of unleaded gasoline and improved fusel oil on engine performance and exhaust emissions were analyzed experimentally. A four-stroke, single-cylinder, spark-ignited engine was used in the experiments. The tests were conducted at a fixed speed and under different loads. The test fuels were blended supplying with fusel oil at rates incremented by 10%, up to 50%. Under each load, the engine's performance and emissions were measured. Throughout the experiments, it has been observed that engine torque and specific fuel consumption increases as the amount of fusel oil in the blend is increased. Nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) emissions are reduced as the amount of fusel oil in the blends is increased.