At present day world researchers are mainly focusing on the different source of fossil fuels instead of petroleum products. Normally, peoples receive biofuels from various renewable sources, example vegetable oils, agricultural wastes, sugar canes and biomass. The sources are attracted for their effect on the air from atmosphere which is maximum carbon-neutral and they are minimum toxic in the common environment. At current stage people are using biodiesel, biogas, and alcohols are the alternate fuels for fossil fuels. Bio fuel is generated from pyrolisis of biomass source. In current days biofuels and their mixture variations (emulsions) are the gifted alternate fuel for DI Diesel Engines. In this research work, we were focusing performance study on the usage of biofuel (Rubber Seed Oil) and biofuel blends with diesel as a fuel in DI Diesel Engine. Mainly we focusing properties of neat rubber seed oil like viscosity, volatility and the boiling point are higher than diesel. In the present work, rubber seed oil and its diesel blends were tested as a fuel in the diesel engine. The blends were prepared in the proportion of 20%, 40%, 60%, 80% and 100% rubber seed oil with diesel fuel. The results pointed out that the reduction in carbon monoxide, hydrocarbons and smoke density were monitored and decreased level of oxides of nitrogen emissions compared with 100% Rupper Seed Oil at maximum load condition. There is decrease in brake thermal efficiency for all the biofuel-diesel blends. It is concluded that the B20 as blend can be used as substitute for diesel fuel with slight decrease in performance and emissions.