Benzene, toluene, ethylbenzene and xylene (BTEX) are produced by combustion of gasoline and diesel. In general, it is known that more than 90% of BTEX is generated in the exhaust system of vehicle. Because it causes diseases such as asthema, preterm birth, and oxidative stress etc., threshold limit value-time weight averages (TLV-TWA) are specified which of benzene is 0.5 ppm, toluene is 50 ppm, ethylbenzene is 100 ppm, and xylene is 100 ppm. So real-time analysis of BTEX is required for prevention of excessive exposure. Ion molecule reaction-mass spectrometry (IMR-MS) is analysis method that ionize gaseous sample through reactant ions and rapidly separates by quadrupole. Real-time analysis of BTEX was conducted by IMR-MS and qualitative/quantitative informations are presented.