Oxidation study, at 700 °C and under controlled atmosphere (oxygen partial pressure: 0.04 Pa) for 24 h, of unimplanted or yttrium implanted pure iron specimens was carried out using in situ X-ray diffraction to observe the yttrium implantation effect. In situ X-ray diffraction analyses performed on unimplanted pure iron clearly show the formation of FeO (wustite) and Fe3O4 (magnetite) compounds at the beginning of the oxidation test whereas the formation of Fe2O3 (hematite) is only detected after 1h30 of oxidation. In situ X-ray diffraction analyses performed with the same experimental conditions on yttrium implanted pure iron show the presence of two Mayn yttrium-iron mixed oxides (i.e. FeYO3 and Fe2YO4) in combination with wustite, magnetite and hematite structures. The presence of the Fe2YO4 compound is important because several authors have reported its anticorrosion properties at high temperature. X-ray diffraction results also show that the formation of FeYO3 and Fe2YO4 is Maynly reinforced at the gas-oxide interface which suggests an outward yttrium diffusion through the oxide layer from implanted pure iron.