The aim of this research is to investigate the effects of ashless dispersant of lube oils on diesel exhaust particles. Emphasis is placed on particle size, morphology, nanostructure and graphitization degree. Three kinds of lube oils with different percentages of ashless dispersant were used in a two-cylinder diesel engine. Ashless dispersant (T154), which is widely used in petrochemical industry, were added into baseline oil at different blend percentages (4.0% and 8.0% by weight) to improve lubrication and cleaning performance. A high resolution Transmission Electron Microscope (HRTEM) and a Raman spectroscopy were employed to analyze and compare particle characteristics. According to the experiment results, primary particles diameter ranges from 3 nm to 65 nm, and the diameter distribution conformed to Gaussian distribution. When the ashless dispersant was used, the primary particles diameter decrease obviously at both 1600 rpm and 2200 rpm. Besides, particles when high percentages ashless dispersant lube oil was used show same chain-like and branch-like cluster. At the nanoscale level, particles show shell-core and urbostratic structures. Particles when higher percentages ashless dispersant lube oil was used show more ordered structures with longer fringe length and lower fringe tortuosity. As to the graphitization degree, the area ratio of the first defect band to graphite band decreases when the ashless dispersant was added into baseline lube oil at both 1600 rpm and 2200 rpm. Particles when higher percentages ashless dispersant was used are likely less relative because of the relatively higher graphitization degree, longer fringe length and lower fringe tortuosity.