The headspace volatiles (HSV) of cooked onions and the odor concentrates of those which were prepared by simultaneous distillation and extraction (SDE) were analyzed by capillary gas chromatography (GC)and gas chromatography/mass spectrometry (GC-MS). As for the HSV analyses, a thermal desorption cold trapping method was used on injection to GC column. Both sliced and whole onion bulbs were used for sample preparation. Boiled, baked and microwave cooked onions were prepared. A total of 50 volatile compounds were identified from these cooked onions. The main component of cooked onion slices was dipropyl trisulfide which was scarcely found in cooked whole onion. Disulfides and trisulfides containing propenyl group were main components of the latter. Furans, including furfural, were the main compounds of baked onion which possessed a very sweet odor. The thermal degradation products of sugars Seemed to contribute to the sweet flavor of cooked onion.