abstract. The effect of iso-butanol addition to diesel fuel on engine performance parameters has been experimentally investigated. The used engine was a single cylinder four stroke CI engine Type Lister 1-8. The tests were performed at engine speed that ranges from 375 to 625 with an increment of 42 rpm at different loads and with 10, 20, 30 and 40% v/v iso-butanol-diesel fuel blends. The overall engine performance parameters measured included air-fuel ratio (AFR), exhaust gas temperature, brake power (B p ), brake specific fuel consumption (bsfc) and brake thermal efficiency (η th ). The experimental results show that AFR, exhaust gas temperature, (B p ) and (η bth ) decreased and bsfc increased with iso-butanol addition compared to net diesel fuel. Also, the obtained results indicate that the engine performance parameters when using up to 30% iso-butanol in fuel blends are better than that of 40%.