Degradation behavior of poly(vinyl chloride) (PVC) was analyzed by means of simultaneous thermogravimetry-mass spectrometry (TG-MS). Weight loss and the production behavior of hydrogen chloride and organic materials with PVC degradation was clearly divided into three stages at lower heating rate. Dehydrochlorination was occurred mainly in the first and second stages. Benzene was formed mainly in the first stage with dehydrochlorination.