In this study, the effect of volatile fractions from engine lubricating oil on diesel particle emissions were studied experimentally. One commercial CF lubricating oil was used and distilled to subtract the different volatile fractions with boiling temperature of 220 °C, 260 °C and 300 °C, respectively. Oils derived from this distillation process were applied as the lubricating oil and following engine experiments were conducted. Diesel primary particles were sampled with a costume designed thermophoretic system. A fast response particulate spectrum equipment was employed to study the size distribution and number concentration of particles in the exhaust. Transmission electron microscopy was used to characterize the size distribution of the primary diesel particles relates to different oil volatile fractions. As to the primary particles morphology, the results show that the high volatile fractions with boiling point lower than 220 °C lead to much more small primary particles than the other fractions. For the particles in the exhaust gas, based on the data from different conditions, the working condition of engine dominate the effects of volatile fractions on the emissions since the temperature changes and leads to different combustion rate of different volatile fractions. In general, under partial load conditions, changing the volatile fractions does not change the unimodal distribution, but under full load condition, remove the high volatile fractions either generate a second strong peak around 100 nm (low engine speed) or varies the single peak positions. Oil volatile fractions also change the number of total, nucleation and accumulation mode particles, and varies with engine load and speed conditions as well.