XPS has been used for investigating the influence of argon ion sputtering on the chemical state and composition of the surface of three iron oxides, Fe₂O₃, Fe₂NiO₄ and Fe₂ZnO₄. XPS spectra of these oxides were measured, while bombardment by argon ions of 3keV were interrupted. The chemical state of the surface of these oxides was found to change from Fe³⁺ to Fe²⁺ by argon ion bombardment, suggesting the reduction of the surface of these oxides. This behavior was attributed to a decrease of the oxygen composition of the surface of these oxides. Then, particular attention should be paid in analysis of a layered structure of oxides formed on the iron and steel surface.