Abstract: Scanning electronic microscope and X-ray energy spectrometer were used to detect the surface structure and chemical component of particulate matter samples from the exhausts of diesel engine fueled with biodiesel and No.0 diesel fuel respectively. The particulate matter from biodiesel engine has less component of dry soot and the diameter is small, so the surface appearance of the conglomerated status looks more compact. While the surface appearance of particulate matter from No.0 diesel exhibits the grape-shaped cohering. Results of elemental analysis reveal that there is only sulfur element in the particulate matter from No.0 diesel. Therefore, biodiesel plays a good role as an alternate to the petrolic diesel.