The thermal stability of five commercial ion-exchange resin catalysts was studied by means of thermal gravimetric analysis (TGA) at elevated temperatures of up to 600 ℃and isothermal temperatures in the range of 150 ℃ and 200 ℃ Resin samples with different initial water contents were also investigated. The study indicated that TGA, as a complementary evaluating method for the plug flow reactor system approach, could be used as a fast analyzing means for study on the thermal stability of ion-exchange resin catalysts. The stoichiometric calculation of the isothermally treated resin catalysts based on the FTIR analysis and acid capacity confirmed that the weight loss of the resins at 150 ℃ and 200 ℃ was caused by the desulfonation process and that desulfonation occurred mainly at the para-position of the benzene ring in the resins. H+ ions and moisture played an important role in the desulfonation process.