To overcome the future energy crisis, vegetable oils can be used as a promising alternative energy source of fuel. Many vegetable oils have been studied with C I engine by modification of oil (Biodiesel) in case of density/viscosity. The blend fuels of diesel with Karanja oil methyl ester (KME) at 10%, 20%, 30% and 40% by volume were prepared to test the diesel engine performance. From the results, performance parameters were found to be very close to that of diesel fuel. The brake thermal efficiency and brake specific fuel consumption are better than diesel fuel for some blending ratios under certain loads. The emission characteristic levels of carbon dioxide, carbon monoxide, nitric oxide and hydrocarbons were found to be higher than pure diesel fuel.