Thermal efficiency and fuel consumption of a Diesel Engine which is main stream of the transportation has to be improved for control of global warming. And a diesel engine is expected to keep the good air quality and health effect, by exhaust emission reduction. Then this paper describes how the variety of Biodiesel Fuel (BDF) and the increase of the BDF mixing ratio reduce CO, HC, smoke and engine-out PN concentration. This paper shows that the PN concentration from the tail pipe is remarkably reduced by after-treatment system.