The purpose of this study is to assess the cause of offensive odor incident that took place at Shin-Gil district in Seoul on 17. Nov. 2007. Air samples were collected from both the inside and outside of the accidental sewage site both at the right after and long after the accident and analyzed by GC/MS method. The results of our initial analysis showed that there were 39 compounds with sufficiently detectable quantities (e. g., above ~ 1 ppb). These compounds can be classified into 3 classes of chemical groups which include: Benzene, Indene, and Miscellaneous. It further indicated that compounds with benzene(C₆H₆) ring were the most abundant species followed by several compounds with indene(C₉H₈) structure. Based on our analysis, we conclude that the release of industrial solvents with indene resin contributed most significantly to the observed malodor incident.