In the course of this work, two iron oxide nanopowder samples (a mixture of FeO / γ-Fe2Ο3-Fe3O4) were composed, implementing the methodology. The synthesis used is a simple thermal decomposition route of organometallic precursors. The organometallic precursor used was the iron acetylacetonate (Fe (acac)3) which underwent reductive thermal degradation. The shape of the nanoparticles was examined and determined by the reaction time and the ratio of the used surfactants, oleic acid (OA) and oleylamine (OAm). The first sample underwent controlled oxidation in the air to transform the non-magnetic FeO phase to a mixture of magnetic phases, while the second sample underwent thermal reduction in a hydrogen atmosphere to produce a composite nanomaterial, with α-Fe, Fe3O4, γ-Fe2Ο3, being the dominant phases.