In many countries, diesel fuel is the most important for use in diesel engines. The use of diesel fuel in this engine would be harmful emissions and cause irreparable damage to the environment.Although various measures is taken to curb pollution such as vehicle inspection programs or control systems installed in vehicle exhaust emissions in developed countries .But these programs is not reduced enough in large cities to the problem of air pollution.In this regard, biofuels have inherent physical and chemical properties that make them in practice, seems cleaner than other fuels. One of the main topics of nanotechnology is materials with new properties and its positive effects, raising the efficiency of current internal combustion engines. In this study,an experimental investigation is carried out to establish the emission characteristics of a compression ignition engine while using cerium oxide nanoparticles as additive in neat diesel and diesel-biodiesel blends. The diesel engine emissions were measured at four engine speed levels (????, ????, ???? and ???? rpm) for the different fuel blends. The results showed that in most blends, the hydrocarbons and carbon monoxide has fallen than diesel fuel.But the amount of nitrogen oxides and carbon dioxide produced by the blend of fuel increased than diesel fuel.