The isothermal decomposition of potassium metaperiodate (KIO4) has been studied as a function of concentration of the dopants chloride, sulphate and barium, by thermogravimetry (TG) in the temperature range 560-580 K. The decomposition data for both pun and doped KIO4 were found to be best described by the Prout-Tompkins (PT) equation. As the dopant concentration increases. the rate of decomposition remains unaffected with chloride, increases approximately linearly with sulphate and passes through a maximum with barium. However, doping did not change the activation energy of the reaction. The results favour an electron-transfer mechanism for the decomposition.