Unsaturated triglyceride oil (sunflower) was obtained from commercial sources. It was epoxidized and characterized by chemical and spectroscopic methods. The thermo-oxidative degradation of poly(vinyl chloride) at 180 °C was investigated. The effects of different metal carboxylate combinations (Ba/Cd and Ca/Zn stearates) in the presence of epoxidized sunflower oil on static heat treatment of PVC have been studied. In order to compare the efficiency of the epoxidized sunflower oil with these metal soap stabilizers, thermal stabilities were evaluated on the basis of evolved hydrogen chloride determined by potentiometric titration and the degree of discoloration are discussed. The development of color and the dehydrochlorination rates were compared for PVC sheets containing epoxidized sunflower oil (ESO) or epoxidized soya bean oil (ESBO). It was found that ESO exerted a stabilizing effect on the degradation of PVC. Furthermore, the thermal degradation of PVC with metal soaps and ESO was investigated by thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG).