Selected properties of commercial iron powders, standardised in the atmosphere of hydrogen, have been studied. The reactivity of iron oxides in the thermal decomposition of KClO4 in the solid-state mechanical mixture of Fe and KClO4 containing 9, 13, 17, 21 and 25wt.% of KClO4, respectively, has been tested by the differential thermal analysis (DTA) and thermogravimetric analysis (TG). It has been established that the Fe3O4 phase on the surface of the iron powder act as an effective catalysts in the thermal decomposition of KClO4.