A study on particulate matter (PM) of a compression ignition engine under partial premixed combustion has been performed. Particularly, the microscopic analyses (SEM and TEM) of several samples at the exhaust were carried out to describe the morphology and ordering degree of particles produced by the combustion of diesel and 15% diesel blended with 85% light hydrocarbon (named DLH). Characterization parameters such as fractal dimension, fringe separation distance, fringe length and fringe tortuosity were analyzed to further study the particle structure. Besides, the particle size distributions at medium and high load were compared. The results demonstrated that the particle size distribution presents as quasi-monodisperse and the average diameter of DLH is smaller than that of diesel. The diesel particles move to a larger size range at higher load, while DLH particles show an obvious shift to smaller particles at higher load, which is related to the competition between surface growth and oxidation rates.