This work studied the formation of highly reactive species in the interface of Fe 0 /iron oxides mixtures, i.e. Fe 3 O 4 (magnetite), γ-Fe 2 O 3 (maghemite) or α-Fe 2 O 3 (hematite) prepared by mechanical grinding and thermal treatment at 200, 400, 600 or 800°C under argon atmosphere. Mössbauer spectroscopy, powder X-ray diffraction, scanning electron microscopy, BET surface area and magnetization measurements suggest a strong interaction between the metal and the oxide surfaces at temperature as low as 200°C, producing highly reactive surface species. These reactive species are readily oxidized when exposed to air at room temperature to form large quantities of Fe 2 O 3 . The treatment at 600 and 800°C leads to an extensive solid state reaction of Fe 0 with Fe 3 O 4 to produce the phase wüstite, FeO, with a strong decrease in BET surface area and reactivity. These thermally treated mixtures Fe 0 /iron oxides were also studied as heterogeneous catalysts to promote the decomposition of H 2 O 2 . The mixtures Fe 0 /Fe 3 O 4 treated at 200 and 400°C showed a remarkable increase in activity for the H 2 O 2 decomposition. The high reactivity of these samples is discussed in terms of Fe surf 2+ species formed by electron transfer from Fe 0 to Fe 3+ at the interface metal/oxide which are active to initiate the H 2 O 2 decomposition via a Haber–Weiss mechanism. The mixtures Fe 0 /γ-Fe 2 O 3 and Fe 0 /α-Fe 2 O 3 ground and thermally treated were also studied, however much lower activities for the H 2 O 2 decomposition were observed.