Abstract In order to decrease the dependency on petrol-originated energy resources, the utilization of different energy resources in internal combustion engines has been the center of interest of researchers. The main renewable alternative combustible species are ethanol, methanol, hydrogen, biodiesel, and biogas. On the other hand, appearing as a by-product during alcohol production via fermentation, the fusel oil is another alternative energy resource which can be used in internal combustion engines. Containing high alcohols, fusel oil is dark brown colored alcohol mixture, and has a strong odor. The calorific value of fusel oil close to other alternative combustible types ones and the limited number of researches on utilization of fusel oil, an alcohol derivative, in internal combustion engines constitute the base of this research. In this study, the effects of the mixture of unleaded gasoline and fusel oil on engine torque, brake specific fuel consumption and exhaust emissions in a single cylinder, spark ignition engine having port-type fuel infection system at various engine speeds and loads have been investigated. As a result of research carried out, as the amount of fusel oil in mixture increased, the improvements have been observed in engine torque at all of engine speeds and loads compared to pure unleaded gasoline. It has been determined that the brake specific fuel consumption and carbon monoxide (CO) and hydro-carbon (HC) emissions have increased while nitrogen-oxide (NO x ) emissions have decreased.