Alcohol, produced from biomass, is used in diesel engines to improve emission. In this study, the effect of adding 3%, 5%, 8%, and 10% (in volume) n-butanol to diesel fuel on the exhaust emission and fuel consumption was investigated on a single cylinder, four-stroke, compression-ignition engine with direct injection. Engine experiments were conducted at full load and at 2400 1/min of engine speed. Tests were repeated for injection pressures of 160, 180, 200 (original pressure), 220, and 240 bar in order to observe the effect injection pressure on the engine. Adding n-butanol to the diesel fuel at small ratios decreased CO, NOR, and soot emissions. The optimum injection pressure in terms of brake specific fuel consumption, CO, HC, and soot emission was determined as 220 bar.