AbstractPVC films were degraded by outdoor exposure, irradiation by a weatherometer and heating by an electric oven. In PVC films subjected to outdoor exposure and to irradiation by the weatherometer at a low temperature, e. g. sample surface temperature of 0°C, photo‐oxidation and scission of the main chain were caused, but dehydrochlorination or formation of solvent‐insoluble substances were not observed. In contrast, PVC subjected to irradiation by the weatherometer at a high temperature, e. g. sample surface temperature of 80°C, showed a degradation tendency similar to that of PVC heated at 200°C in the electric oven, and decomposition of the thermal degradation type characterized by dehydrochlorination, formation of polyenes and formation of solvent‐insoluble substances were