Abstract: In order to investigate why particle emissions are reduced when butanol-diesel fuel is burned in diesel engines, the characteristics of particles emitted from burning different butanol-diesel blends in diesel engines were systematically studied to analyze the principles of composition, size distribution and microstructure of the particles using thermal analysis and field emission scanning electron microscope technology. The butanol was added into the blend with three kinds of mass percentages:0(B0), 5%(B5), 10%(B10). It was observed that particles of different butanol-diesel blends all demonstrated cluster structures, and they became more compacted with the rising butanol percentage. In addition, the aggregation degree was larger. Moreover, the particle size decreased with the improvement of butanol percentage; the sizes were 1.43,0.85 and 0.52 μm with butanol-diesel blends of B0, B5 and B10. The main component of the particles was soot, which accounted for approximately 60% of the total particle mass. With the increase of butanol ratios, the proportions of soluble organic fraction (SOF) and soot were increased, while sulfates, metals and other non-volatile components decreased gradually. The results showed that particle transformation was stimulated, and the oxidation process was substantially improved, with the addition of butanol. Plus, the size distribution of particles was smaller figure than with no butanol added. The proportion of SOF on the surface of the particles was increased, which increased the coagulation probability in collision situations among particles; the particle size decreased and agglomeration was improved as a result.