The viscosities of raw vegetable oils are quite higher than diesel fuel. To lower the viscosity, sunflower oil methyl ester was mixed with diesel fuel and then tested in a single-cylinder, four-stroke, air-cooled diesel engine as an alternative fuel. The study examines short-term engine tests with sunflower oil methyl ester fuel compared to number 2 diesel fuel (No. 2 D). Engine tests were carried out fully loaded at different speed ranges. The engine torque and power of sunflower oil methyl ester-diesel fuel blend was lower than that of diesel fuel in the range of 6-9%, and specific fuel consumption was higher than that of diesel fuel by approximately 3%. CO2, CO, and NOx emissions of sunflower methyl ester were lower than those of diesel fuel.