Abstract: Effects of several 6-aminouracils on heat stability of PVC were investigated by an oven discoloration method.The results indicated that the heat stability of PVC was improved with an increase of electronwithdrawing capability of groups linked to the carbamido groups.Based on this progressive change law of heat stability as well as molecular structural characteristics of 6-aminouracils, it was predicted that 6-aminouracils could stabilize PVC by an electrophilic reaction with PVC through their 6-C atom as the electrophilic center.This means that the classical Frye and Horst’s theory are not suitable for the heat stabilization mechanism of 6-aminouracils, and therefore, the exact mechanisms for this new heat stabilizer should be clarified in further work.