Our environment is faced with serious problems related to the air pollution from automobiles in these days. In particular, the exhaust emissions of diesel engines are recognized as main causes of the air pollution. CRDI (common rail direct injection) diesel engine is widely used for the sake of minimization on exhaust emission. Because biodiesel fuel is a renewable and alternative fuel for diesel engine, its usability is expanded. An commercial CRDI diesel engine used to commercial vehicle was fueled with diesel fuel and 5% biodiesel blended fuel (BDF 5%) with city mode in excess of 300 hours. The engine performance and exhaust emissions were sampled at 1 hour interval for analysis. To check the engine parts (valve, injector), the engine was inspected after test. It was concluded that there was no unusual deterioration of the engine, or any unusual changes in engine power and exhaust emissions in spite of operation of 300 hours with BDF 5%.