A　series　of　stearates　with　different　rare-earth　ion　were　investigated　as　thermal　stabilizers　for　rigid　PVC　at　180　degrees　C　in　air.　Their　stabilizing　efficiency　was　based　on　measuring　the　rate　of　dehydrochlorination.　The　resulted　revealed　the　higher　stabilizing　efficiency　of　the　investigated　rare-earth　stearates　as　thermal　stabilizers　for　rigid　PVC　compared　with　the　thermal　stabilizers　for　industry:　calcium　stearate,　zinc　stearate,　butyl　stannum　mercaptide,　phosphite　esters,　beta-diketone　and　epoxidized　sunflower　oil.　This　was　well　illustrated　by　longer　incubation　period　(T-s)　values　and　lower　rate　of　dehydrochlorination.　The　stable　efficiency　was　affected　by　the　nature　of　rare-earth　element＇s　individual　electronic　shell.　The　mechanism　for　the　stabilizing　effect　of　rare-earth　stearates　was　proposed.　The　result　was　experimentally　proved　based　on　IR　spectrum.