Abstract: The effects of calcium, strontium, barium, zinc and cadmium salts of monobutyl malonate, succinate and maleate on the heat stability of poly(vinyl chloride) (PVC) were determined by an oven discoloration method. The results indicated that the discoloration rate of PVC stabilized with dicarboxylic acid monoester metal salts decreased with an increase of the positive electricity of carbon atom in carbonyl groups and the polarization force of metal ions in the molecules. However, PVC stabilized with dicarboxylic acid monoester metal salt containing a dienophilic structure presented a weaker coloring effect. It was deduced that the reduction mechanism of discoloration rate for PVC by dicarboxylic acid monoester metal salts was attributed to the electrophilic reactions of carbon atom in carbonyl groups and metal ions with PVC. Moreover, the DielsAlder cycloaddition reaction led to the weak coloring effect on PVC when stabilized with dicarboxylic acid monoester metal salt containing a dienophilic structure.