The chemical states of tin and iron atoms were investigated by Mössbauer spectroscopy on oxide films (of various thicknesses) formed on a Zr-1.3% Sn-1% Fe-0.5% Cr-0.12% O alloy (enriched with ¹¹⁹Sn and ⁵⁷Fe) in an autoclave at 633 K with 10 ppm Li and 650 ppm B. Specimens were analyzed by Conversion Electron Mössbauer Spectroscopy (T = 298 K) and γ-ray transmission (T = 298 and 77 K) modes to investigate the surface and the bulk of the oxide films, respectively. The main results on the oxide were as follows: • For tin atoms: Sn²⁺ and Sn⁴⁺were clearly identified. In addition, metallic β-Sn was greatly suspected. • For iron atoms: Zr(Fe,Cr)² precipitates, α-Fe, Fe³O⁴, Fe²⁺, and Fe³⁺, were clearly detected. Moreover, it was shown that during the oxide film growth the chemical states of tin and iron atoms change, in particular after the kinetic transition.