A CRDI diesel engine used to commercial vehicle was fueled with 20% biodiesel fuel(BDF 20) in excess of 150 hours. Engine dynamometer testing was completed at regularly scheduled intervals to monitor the engine performance and exhaust emissions. The engine performance and exhaust emissions were sampled at 1 hour interval for analysis, Also, BSEC with BDF 20 resulted in lower than with diesel fuel. Since the biodiesel fuel used in this study includes oxygen of about 11%, it could influence the combustion process strongly. So, BDF 20 resulted in lower emissions of carbon monoxide, carbon dioxide, and smoke emissions without special increase of oxides of nitrogen than diesel fuel. It was concluded that there was no unusual deterioration of the engine, or any unusual change in exhaust emissions from using the BDF 20.