In this study, the concentrations of major odorous compounds including reduced sulfur compounds (DMS, $CS_2$, and DMDS) and aromatic VOC (benzene, toluene, xylene, etc.) were measured continuously using an on-line GC analytical system. Our measurements were made from a residential area of Ansan city during about two weeks period of October, 2004. The highest mean concentrations of reduced S and VOC were recorded as 56.9 ppt of DMS and 21.7 ppb of toluene, respectively. The results of this study generally show that the pollution levels for both types of chemicals are significant relative to previous measurement results reported from comparable sites, if the results are compared simply in terms of the magnitude of the measured concentration data. Moreover, when the relative importance of different compounds is compared in terms of the odor strength, it indicates that the contribution of reduced S compounds may be much more important than that of VOC in the study area.