Adding bio-fuels to pure diesel may reduce the environmental harming but on other hand, the performance of the combustion would influence. The aim of this study is to present an investigation results on the effects of sunflower oil blend to pure diesel on the performance of single cylinder compression ignition engine. Three mixtures included sunflower oil/diesel ratios of 5:95, 8:92 and 11:89 in addition to pure diesels as a base, were tested. The experimental tests were carried out by using four stroke engine with a single-cylinder and 21:1 compression ratio. The engine performance was measured at various operating conditions. The results indicated that when sunflower-diesel fuel mixture used, the brake power of the engine slightly decreased while, the brake thermal efficiency showed decrease compared with diesel fuel. At the same time, it was found that break specific fuel consumption also increased compared with the pure diesel fuel. The exhaust gas temperature was decreased compared with the case of using pure diesel fuel. © 2012 Asian Network for Scientific Information.