To examine the efects of fuel properties on auto-ignition in diesel engine, we have studied hte physical properties and the chemical composition of donestic automotive diesel fuel and have measured its cetane number using CFR(Cooperative Fuel Research Committee) engine. It is found that the cetane number is related to the physical properties such as specific gravity and boiling range distribution, and to the saturates and aromatic contents of diesel fuel. Therefore, it is suggested that in the refining processes the factors affecting the saturates and aromatic contents of diesel fuel. Therefore, it is suggested that in the refining processes the factors affecting the cetane number stated above should be taken into account to improve the autoignition property of automotive diesel fuel.