Abstract: A series of poly alkylene succinate was synthesized by ester exchange reactions and the solid electrolytes were made from the polyesters and lithium perchlorate. Thermal decomposition of the polymers and their electrolytes was explored with thermal gravimetric analysis and their kinetics of thermal decomposition is studied. The results show that the decomposition temperature for the polyesters is nearly the same and is not related to the length of the chain units; thermal stability of polyester electrolytes is worse than that of the polyester and decreases with the increase of salt concentration in the electrolytes. The pyrolytic fragments of poly (tetramethylene succinate) and its electrolyte were determined with GC/MS combined technique. The decomposed products of the polymer are different from those of its electrolyte. Finally, the separate decomposition mechanisms for the polyester and its electrolyte are suggested in this article.