A wuestite phase metastable at room temperature in the form of a whisker conglomerate was found on the surface of nanoporous iron obtained by electrochemical dealloying (selective anodic dissolution of a less noble metal) of ferromanganese. The features of the further oxidation of iron by TG-DSC and Х-ray phase analysis with a temperature sweep were studied. A wide range of coexistence of three forms of iron oxides and relative stability of the magnetite phase up to 900°C were described.