This study presents the characteristics of exhaust diesel particles with fuel injection types and after-treatment technologies on diesel engines. The influence of injection methods (direct injection and common rail direct injection) and the equipments of diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) on exhaust particle were investigated. Size distributions were measured for various engine loads using an ejector-type diluting sampler and a scanning mobility particle sizer (SMPS). Both low sulfur diesel (LSD) and ultra low sulfur diesel (ULSD) fuels were used to compare the effect of sulfur compounds on exhaust particle formation. Oxidation catalyst slightly reduces the accumulation mode in all operating modes, but contributes to increase the nuclei mode at high load condition. Diesel particulate filter eliminates most of particles in all conditions except for the nuclei mode particles at high load. This phenomenon is probably due to the formation of SO3 from the oxidation of sulfur compounds of fuel after the oxidation catalyst. With ULSD, most of particles were trapped by a DPF system at all operating modes.