The thermally induced solid-state syntheses of γ-Fe₂O₃ nanoparticles from iron-bearing materials (FeSO₄, Fe₂(C₂O₄)₃ and almandine garnet) are described. Magnetic properties, particles size and the mechanism of the structural change of γ-Fe₂O₃ nanoparticles have been investigated using ⁵⁷Fe Mössbauer spectroscopy, X-ray powder diffraction (XRD) and atomic force microscopy (AFM). γ-Fe₂O₃ nanoparticles are transformed into hematite via ε-Fe₂O₃ as the intermediate.