Abstract: The heat stabilization of dialkyltin carboxylates on PVC was studied. It was found that the stronger the electron-withdrawing of the group linked to carbonyl C atom in the stabilizer, the more stable of PVC resin. For the dialkyltin carboxylate, the stabilizing ability was originated from the electrophilic reaction between PVC and the electrophilic centers of the carbonyl C atom in the carboxylate radical and/or dialkyltin ion. For this reason, the traditional Frye and Horst’s theory on mechanism of heat stabilization of heat stabilizers did not apply to dialkyltin carboxylates.