Thermal stability of polyaniline tosylate was studied at 150, 200 and 250-degrees-C in air and nitrogen atmosphere. The thermal deterioration in conductivity is a function of time/temperature exposure and atmosphere. Polyaniline tosylate is stable to 250-degrees-C for short intervals in nitrogen without appreciable loss in conductivity. Its conductivity is seriously affected in air atmosphere. In air atmosphere, oxidation and possible structural rearrangement lead to loss in conductivity at temperatures below thermal decomposition.