This paper investigates the impacts of using n-butanol-diesel fuel and ethanol-diesel fuel blends on engine performance, exhaust emission, and cycle-by-cycle variation in a Diesel engine. The engine was operated at two different engine speed and full load condition with pure diesel fuel, 5% and 10% (by vol.) ethanol and n-butanol fuel blends. The coefficient of variation of indicated mean effective pressure was used to evaluate the cyclic variability of n-butanol-diesel fuel and ethanol-diesel fuel blends. The results obtained in this study showed that effective efficiency and brake specific fuel consumption generally increased with the use of the n-butanol-diesel fuel or ethanol-diesel fuel blends with respect to that of the neat diesel fuel. The addition of ethanol or n-butanol to diesel fuel caused a decrement in CO and NOx emissions. Also, the results indicated that cycle-by-cycle variation has an increasing trend with the increase of alcohol-diesel blending ratio for all engine speed. An increase in cyclic variability of alcohol-diesel fuel blends at low engine speed is higher than that of high engine speed.