In recent research, decreasing oil consumption and using a synthetic oil have been shown to be effective methods of reducing smoke emissions. However, the investigation of the constituents of white smoke and its environmental effect on humans have not been undertaken. The purpose of this investigation is to clarify the characteristics and compositions of white smoke and to analyze its environmental effect on humans using Ames test, and to evaluate a control for reduction of emitted matter by steady-state engine tests.Emitted matters(EM) from synthetic oil is less than that of semi-synthetic and mineral oils under the same test conditions. Emission after treatment resulted in the lowest EM when simulating the results of the ISO 6460 test, which results showed a decrease to about 1/10.EM from two-stroke engine mainly consists of unburned engine-oil and more than 95 % of EM is soluble organic fraction (SOF). Ames test results showed mutagenic responses and mutagens in TA100(+S9mix) were stronger than those in TA98(-S9mix). This characteristics is different from the results using diesel SOF extracts.From the results above, the authors defined the unburned-oil particulate matters from two-stroke engine as “O-PM” in order to separate the diesel PM which mainly consists of dry soot.