Automobile exhaust is considered to be an important emission source of air pollutants; it is thought that measurements of Hazardous Air Pollutants (HAPs) concentrations are important for the reduction of HAPs in atmospheric environment. Proton Transfer Reaction/Mass Spectrometry (PTR/MS) has been applied for measurements of HAPs in the atmospheric environment, because of high sensitivity detection in real time. Then, PTR/MS was investigated concerning a possibility of being used for on-line-real-time measurement of the HAPs exhaust from automobiles. Gasoline was analyzed in combinations of GC and PTR/MS, and it was clearly shown that a few interference ions are generated from other compounds. Moreover, automotive exhaust concentration measurements become difficult due to a reduction of emission concentration, it is very important to know the availability that the sub ppb order compounds can be detected by PTR/MS.