In this study, the concentrations of offensive odorous compounds seasonally emitted from the chemical plant at Chongju industrial complex in Korea were determined by the analytical methods of gas chromatography, high performance liquid chromatography and uv/vis spectroscopy. The kinds of offensive odorous compounds examined are formaldehyde, acetaldehyde, butyl aldehyde, propion aldehyde, n-valeric aldehyde, iso-valeric aldehyde, hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, trimethyl amine and ammonia. The seasonally emission levels of all odorous compounds except dimethyl sulfide at 13 sampling points of plant were lower than those of the regulation standard levels of the industrial complex in Korea. The levels were the highest in June, and lowest in December. The propion aldehyde and iso-valeric aldehyde in June and December, butyl aldehyde in December, and n-valeric aldehyde were not detected in all the three seasons at any sampling points of the plant examined. But in June, dimethyl sulfide was emitted up to 16 times than that of the regulation level.