This study discusses the suitability of iso-butanol/diesel fuel blends as an alternative fuel and determines their effects on the performance and combustion characteristics of a heavy-duty diesel engine. For this purpose, various iso-butanol/diesel fuel blends containing 5%, 10% and 15% iso-butanol were prepared in volume basis and tested in a turbo-charged, six-cylinder direct injection diesel engine at the speed of 1400 rpm and three different loads (150, 300 and 450 Nm). The results indicate that when the test engine was fueled with the iso-butanol/diesel fuel blends, the brake thermal efficiency decreased, while the brake specific fuel consumption increased with proportion to using conventional diesel fuel. When iso-butanol/diesel fuel blends were used, the heat release rate, the peak cylinder gas pressure slightly increased compared to the neat diesel fuel use. Although the iso-butanol/diesel fuel blends have poor performance values at partial engine loads, their fuel properties affected the combustion and injection characteristics. They caused reductions in CO, NO_x emissions and smoke opacity. However, unburned HC emission slightly increased.