Iron oxides are widespread compounds in nature and usually contain metal cations other than iron incorporated in their structure [1]. Also, doping of synthetic iron oxides with different metal cations can improve their properties (magnetic, electric, catalytic, photocatalytic, optical, gas sensing, etc) which can be essential for their applications in advanced technologies. In the present work properties of goethite (α-FeOOH) and hematite (α-Fe2O3) doped with non-magnetic In3+ ions were investigated. Indium-doped goethite samples were synthesized by a precipitation method at pH 12 using a strong organic alkali tetramethylammonium hydroxide (TMAH) for pH adjustment [2,3] Prepared samples were analysed using 57Fe Mössbauer spectroscopy and other instrumental techniques. Maximum In-for-Fe substitution in goethite at about 8 mol% was estimated by the measurement of the unit cell expansion (XRD) and the reduction of the hyperfine magnetic field (Mössbauer spectroscopy) [3]. In-doped hematite samples were prepared by calcination of In-doped goethite samples at 500 °C [5]. An increase in size of hematite unit cell and a decrease in the hyperfine magnetic field suggest In-for-Fe substitution in the structure of hematite.