The backbone of the economy of a nation is dependant of surface transport. Thus diesel engines play a vital role as prime movers. The recent energy trend offers a challenge as well as an opportunity to look for substitutes of fossil fuels for both economic and environmental benefits. Investigation and development of bio-fiiels as an alternative and renewable source of energy for transportation has become a major target in the effort towards energy self-reliance. Bio-fuel commands crucial advantages such as technical feasibility of blending, superiority from the environment and emission reduction angle, its capacity to provide energy security to remote and rural areas and employment generation. Moreover, Bio fuel will also provide rich bio mass and nutrients to the soil. This paper presents the results of performance and emission analyses carried out in an unmodified diesel engine fueled with rice bran oil methyl ester (biodiesel) blends with diesel. Engine tests have been conducted to get the comparative measures of brake thermal efficiency, specific fitel consumption and emissions such as CO, HC, NOx to evaluate the behavior of biodiesel and diesel in varying proportions. The results reveal that blends of rice bran methyl ester with diesel up to 20% by volume (ZOBD) provide better engine performance and improved emission characteristics.