The ultra-fine particles emitted by automobile are emerging issue because it is known to have adverse human health effect. Particles emitted from automobile and other engines are a complex mixture of elementary and organic carbons and other chemicals. Especially diesel particles are mainly composed of elemental carbon (soot) and volatile compounds derived from unburned and partially burned fuel, and lubricating oil and sulfate. More than 90% of particle number is usually in the ultra-fine particle size range. Ultra-fine particles are known to have increased ability to cause pulmonary inflammation. Adverse health effect may be explained by the greater surface area of the ultra-fine material, which delivered oxidative stress because of a greater surface for the generation of free radicals by as yet unknown mechanisms, or for release of redox-active transition metals and organics. In conclusion, over the past decade attention has been paid on physical/chemical characteristic, mechanism, toxicity, health effects, however, we do not have enough information about ultra-fine particles. So we need to conduct continuous research and management on ultra-fine particles.