The oxidation behavior of Fe50Ni50alloy foils implanted with 80‐keV N+2ions at a dose of ∼1016ions/cm2is studied by using the technique of conversion electron Mo¨ssbauer spectroscopy (CEMS). The oxidation is carried out in air at various temperatures up to a maximum of 500 °C, for different intervals of time. It is shown that the as‐implanted as well as implanted and annealed foils exhibit higher resistance to oxidation as compared to the virgin foils; the oxidation resistance being significantly higher in the case of the annealed foils. It is established that the reason for improvement in oxidation resistance is nickel enrichment of the surface layers leading to formation of diffusion‐limiting nickel‐rich NixFe3−xO4phase at the oxide‐metal interface during the early oxidation process. The presence of this phase in the oxidized samples is inferred from the hyperfine interactions exhibited by the corresponding CEMS spectra and also from x‐ray diffraction measurements.