In order to study the effects of blending biofuel and heavy oil on the particulate matter emission characteristics of marine engines, experimental studies of load characteristics（E2）and recommended characteristics（E3）were carried out on a two-stroke marine engine. Five fuels including B15 biofuel（i.e., a fuel blend of biodiesel and 180 marine low-sulfur heavy fuel oil（HFO）mixed in a mass ratio of 15%∶85%, and so on）, B24 biofuel, B30 biofuel, B50 biofuel, and 180 marine low-sulfur HFO were selected. The quantitative concentration of particulate matter in the exhaust gas at different particle sizes was measured by a particle sizer, and the results showed that the total number of particles in the accumulation mode（greater than 50 nm）of biofuel was reduced or converted into particles of a smaller nuclear mode（less than 50 nm）compared to 180 marine low-sulfur HFO. The emission factor of particulate matter was measured and calculated by membrane weighing, and it was found that the emission factor of particulate matter decreased as the proportion of biofuel oil increased under the load characteristic cycle condition. The particulate matter samples were collected by a thermophoresis probe, and the microscopic appearance of the particles was observed with transmission electron microscopy（TEM）. And it was found that particulate matter aggregates exhibited a chain-like structure.