In this paper, the characteristics of particle size distribution in the exhaust gas of a diesel engine lubricated by two kinds of lubricating oil are investigated. The experiments are conducted in a turbocharged direct-injection diesel engine with Fast Particulate Spectrometer DMS 500 connected to the exhaust pipe. Two kinds of commonly used commercial lubricating oil, Kunlun API CF-4 15W40 and Mobil API CI-4 15W40, are chosen for the experiments. Particle size distribution and total number concentration are measured under medium load (100 Nm) and full load. Barring a few exceptions, the results indicate that total particle number concentration is almost the same, while particle size distribution shows great difference. CD (C) 2012 Elsevier B.V. All rights reserved.