A perfluoro-sulphonate-ionomer membrane (Nafion-117), incorporated with inorganic ion exchanger (IIE), was evaluated using thermogravimetric analysis and FT-IR spectroscopy to ascertain its thermolytic degradation behavior. The two-step decomposition shown by derivative scans in the Nafion-polyantimonic acid composite was studied by obtaining FT-IR spectra of thermally treated specimens under dynamic conditions up to 200 degrees, 350 degrees and 400 degrees C. Similar studies were carried out for Nafion-zirconium phosphate and Nafion-zirconium oxide composites. Incorporation of IIE invariably decreased the thermal stability of the perfluoro polymer matrix of Nation. However, the decomposition patterns of -SO3H groups remained unaffected. Comparative studies of the TGA and DTA scans of these composites show presence of water of crystallization in the incorporated IIEs.