Microstructure and size of particle emitted from the three-cylinder, direct injection diesel engine were investigated by using HRTEM under two fuel supply advance angles, two operating conditions and two kinds of proportions of biodiesel/diesel blends. The results indicated that under the research conditions, spherical primary particles consisted of the particles generated by the combustion of the fuels. The particles exhibited the different shapes and characteristics of fractal structure. The primary particles have multilayer graphite-like microcrystal structure. The diameters of primary particle for B0 and B20 are ranged between 25.6~31.3nm and 28.7~40.0nm, respectively. Mean diameter of primary particles of B20 is larger than that of B0.