??The combustion efficiency in diesel engine and its fuel economical are excellent. On the emission side, it has been shown that the exhaust gases from diesel engine became the cause of air pollution problem rather than the gasoline engine. It is strongly needed to reduce the emissions on PM and NOx as the main pollutant on diesel engine. It demands the alternative fuels to achieve the emission gas reduction. The bio-diesel fuel has advantages in the view point of air pollution improvement. Bio-diesel can be made from cooking and vegetable oil. In the engine performance experimental results, it is observed that the highest maximum pressure inside combustion chamber was achieved by BD50, followed by BD25 and diesel fuel. At 2000 rpm the maximum pressure of all tested fuels were relatively same. The heat released showed a similar trend to that of maximum pressure. The IHP of BD50 was clearly higher than BD25 and diesel fuel at all engine speed. However the BHP of BD50 was slightly higher than BD25 and diesel fuel. The indicated mean effective pressure of all tested fuels showed the obvious difference with BD50 had highest IMEP, followed by BD25 and diesel fuel. From the emission measurement, it is shown that the emission characteristics of exhaust gas is strongly affected by the blending ratio of diesel and bio-diesel. The NOx emissions increased by increasing of bio-diesel content. The NOx emission of BD50 was significantly higher than diesel fuel. However this difference was smaller at higher engine speed. On the other hand, the use of bio-diesel decreased the CO emission significantly at all tested engine speed. The measurement of exhaust gas temperature showed that the exhaust gas temperature of BD25 and BD50 were significantly lower than that of diesel fuel. As brief conclusion for engine performance and emission test, the bio-diesel can be used for alternative fuel for conventional diesel. It produced similar power compared to diesel fuel; and lower CO emissions compared to diesel fuel though the NOx emissions is higher than the diesel fuel.