Abstract: In order to study the effects of engine loads and proportions of biodiesel/diesel blends on the particulate emissions, morphology and microstructure of particulates emitted from an electronic controlled high pressure common rail diesel engine were investigated by using HRTEM under the two operating conditions of rotation speed at 2 000 r/min and torque at 75 N?m and 2 000 r/min and 225 N·m, and four kinds of proportions of biodiesel/diesel blends (B0, B10, B50 and B100). The results indicated that the primary particles generated only by B100 present irregular shape and very different particle sizes. However, the spherical primary particles consisting of the soot generated by the other fuels are typically monodisperse. The primary particles have multilayer graphite-like microcrystal structure. There exists torsion and translation between the carbon lamella. Disordered core zone is inside the primary particle. Under the operating condition of 2 000 r/min and 225N·m, the mean diameter of primary particle for B100 was 45.57 nm and very different from the other three fuels. Engine loads and proportions of biodiesel/diesel in the blends which were lower than 50% have little influence on the mean diameter of primary particle. The results can provide references for the formation mechanisms of diesel particulates and the design of after-treatment system.