Organic compounds of particulates accumulated in the tunnel duct of freeways were extracted with a benzene-ethanol mixture solution (4 : 1, v/v) and fractionated into four fractions by 5% hydrous silica gel. The obtained organic substances were found to be composed of nonpolar, semipolar, polar and high polar compounds, by the use of GC-MS. The nonpolar fraction, in which linear alkanes ranging from C₁₆ to C₂₆ dominated, was shown to have many peaks on an extremely broad peak by GC-MS. These notable patterns were similar to those of vehicular exhausts. These observations have been characteristic of GC patterns of vehicular exhausts. The semipolar fraction was identified to contain mainly three- to four-ring polycyclic aromatic hydrocarbons (PAHs) such as phenanthrene, dibenzothiophene, fluoranthene, pyrene and chrysene/triphenylene. Their concentrations in the total mass of particulates showed 0.6-39.5 μg/g. Moreover, alkylated PAHs such as benzo [b] naphtho [2, 1-d] thiophene and cyclopenta [cd] pyrene also detected in the sample, might be used for the markers of automobile exhaust particulates. In this fraction, 64 PAHs were tentatively identified by the use of the Wiley library search system and some of them were identified finally in comparison with authentic samples by GC-MS. The polar fraction was found to include oxygenated polycyclic aromatic compounds such as 1-naphthaldehyde, phenanthrene-9-carboxaldehyde, 9-fluorenone, xanthone, benzanthrone, anthraquinone, 9, 10-phenanthrenequinone, 2-methylanthraquinone and 1, 2-benzanthraquinone. Their concentrations ranged 0.9-51.7 μg/g in the total mass of particulates and were higher than those of oxygenated PAHs in particulates collected in a rural area, urban air and indoor air. In this fraction, 44 oxygenated compounds including oxygenated polycyclic aromatic compounds were tentatively identified by the same technique described above. The high polar fraction could not be analyzed.