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 parallell 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 framework, while Yst and Dyst's effect is not clear.