The aim of this research is to investigate the effects of ashless detergent dispersant of lube oils on diesel particles. Emphasis was placed on particle size, morphology, nanostructure and graphitization degree. Three kinds of lube oils with different percentages of ashless detergent dispersant were used in a two-cylinder diesel engine. 4.0 wt. % and 8 wt. % ashless detergent dispersant (T154), which is widely used in petrochemical industry, were additivated into baseline oil to improve the performance respectively. A high resolution Transmission Electron Microscope (HRTEM) and a Raman spectroscopy were employed to analyzed and compared particle characteristics. According to the experiment results, primary particles diameter ranges from 5 nm to 70 nm, and the diameter distribution conformed to Gaussian distribution. With the using of this additive, the primary particles diameter decrease slightly at both 1600 rpm and 2200 rpm. Besides, particles from high percentages ahsless detergent dispersant lube oils show same chain-like and branch-like cluster with particles from the baseline lube oil. At the nanoscale level, particles show shell-core and urbostratic structures. Particles from higher percentages ahsless detergent dispersant lube oils 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 decreased when the ashless detergent dispersant was added into baseline lube oil at both 1600 rpm and 2200 rpm. Particles from higher percentages ashless detergent dispersant are likely less relative because of the relatively higher graphitization degree, longer fringe length and lower fringe tortuosity.