The electrochemical behaviour of pure iron anodes in molten KHSO4 at 250°C was studied. Typical passivity phenomena were observed under potentiostatic as well as galvanostatic runs. A transition time related to the onset of full passivity was determined. The passive film was studied by X-ray diffraction. Its average structure corresponded to Fe3O4. The mechanisms of passivation and corrosion of passive iron are discussed on the basis of behaviour of passive iron in aqueous systems.