The thermal degradation of some sulfonic cationites namely Amberlite IR-120, Indion-223 and Indion-225 was investigated using instrumental techniques like thermal analysis (TG) and Scanning Electron Microscopy (SEM). Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the resins degradation steps. The sulfonic cationites undergo degradation through dehydration, followed by decomposition of sulfonic acid functional groups liberating SO 2 . The thermogravimetric analysis of above cationites at higher temperature up to 520˚C, show mass loss of 61.61% and 25.43% respectively for Indion-223 and Indion-225, while Amberlite IR-120 cationite get burned off completely.