The thermal degradation of polyvinylchloride has been investigated by several workers, and different mechanisms have boon suggested for the degradation. In the thermal degradation of ITC, hydrochloric acid is evolved and a coloured residue is left. In the present work, the problem was tackled in four different ways. The main aim was to assign a definite mechanism for the degradation. Commercial polymer prepared by suspension method, Geon 111 (JLB-49) was used for these measurements. The influence of solvents on the degradation was investigated by carrying out the dehydrochlorination in presence of different solvents. The acid evolved was estimated by titrating it against standard caustic soda solution. The solvents used were, benzophepnone, dioctylphthalate, dichloronaphthalene, benzyl alcohol, tritoluylphosphate and ethyl benzoate. It was observed that solvents have an influence on the dehydrochlorination, the rate being greatest in benzophenone and tritoluylphosphate. An attempt has been made to explain these effects.