Structural　characterization　of　rare-earth　stearate　was　conducted　by　FTIR　and　XRD.　The　results　show　that　the　bonds　between　the　stearate　and　rare-earth　metal　ions　in　rare-earth　stearate　are　main　ionic　character　and　have　the　stratified　crystalline　structure　with　the　crystal　layer　formed　from　a　plane　layer　of　rare-earth　ions　combined　with　two　layers　of　fully　extended　zigzag　chains　of　stearic　acid　radicals　arranged　parallelly　to　each　other　on　its　both　sides,　and　the　rare-earth　ions　axes　are　inclined　to　the　crystal　layer　planes　in　it.　Congo　red　test　showed　that　the　stabilizing　time　increased　when　the　stabilizers＇　concentration　increased.　The　order　of　stability　of　this　four　rare-earth　stearates　is　Last　＞　Ndst　＞　Yst　＞　Dyst.　Furthermore,　the　thermal　stability　mechanism　of　rare　earth　stearate　for　PVC　has　been　presumed　by　FTIR.　The　results　indicate　that　Last　and　Ndst　can　bate　the　chain　reaction　and　exchange　the　labile　functional　groups　in　the　backbone　chains　for　other　more　stable　substituents　derived　from　the　stabilizer　and　change　the　framwork,　while　Yst　and　Dyst＇s　effect　is　not　clear.