A novel thermal stabilizer poly(dioctyltin maleate-styrene-methyl acrylate) [P(DOTM-St-MA)] was synthesized by radical solution polymerization with benzene as the solvent and 2,2-azobisisobutyronitrile as the initiator. The structure of terpolymer was characterized by FTIR and H-1-NMR spectra, and thermal stability of the stabilizer was measured by thermogravimetric analysis (TGA). Evaluation of [P(DOTM-St-MA)] as thermal stabilizer for poly(vinyl chloride) (PVC) was measured by acidimeter, and the extent of changing color of PVC was measured by thermal aging method. Compatibilities of four stabilizers with PVC were characterized by scanning electron microscope (SEM). The results showed that, with the same tin content in PVC mixtures, [P(DOTM-St-MA)] exhibited better performance as a PVC stabilizer compared with other stabilizers, such as poly(dibutylin maleate-styrene-methyl acrylate), DOTM, and dibutylin maleate (DBTM). Furthermore, [P(DOTM-St-MA)] had better compatibility with PVC in PVC processing. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1216-1222, 2009