In the present days the fuels are limited and depleting day by day as the consumption is increasing very rapidly. And also due to these fossil fuels the world today is facing a serious environmental pollution. To avoid this it is necessary to find an alternative fuel to Diesel which should be produced from renewable resources. The fuels which are produced from these resources are termed as alternative fuels. In the present work, experimental investigations were carried out on a single cylinder 4-stroke, naturally aspirated, direct injection and water cooled CI engine with Diesel and waste vegetable biodiesel blends as fuel. From this Brake Thermal Efficiency (BTE), Brake specific fuel consumption (BSFC) and Exhaust Emissions were studied. From the experimental results it is observed that obtained Brake Thermal Efficiency is better for bio-diesel blend B20 with minimum Brake Specific Fuel Consumption. It is also observed that there is a reduction in the quantity of Carbon Monoxide and Hydro Carbon and increased exhaust gas temperature when compared with Diesel as fuel.