X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray scattering (GIXS) have been used for characterizing thin oxide films formed on Fe-10 ∼ 90mass%Cr alloys by heating at 873 K in air. The XPS depth profiles indicate that the oxide film of Fe-10mass%Cr alloy consists of mainly an iron oxide, and a chromium oxide is predominant in the oxide film formed on alloys with chromium more than 50mass%. In Fe-30mass%Cr alloy, the oxide film consists of a two layered structure; iron rich oxide in the outer layer and chromium rich oxide in the inner layer. The thickness of the oxide films appears to be insensitive to the bulk chromium concentration in the range between 30 and 90 mass% under the present oxidation condition. The GIXS results identify the main crystallographic structure of the oxide film with corundum (Fe 2 O 3 or Cr 2 O 3 ) type structure, although it includes the preferential orientation and depends on the bulk chromium concentration.