&nbsp;&nbsp;The effect of an aluminizing treatment on the oxidation behavior of carbon-nitrogen free Fe-12Ni-9Co-10W alloy has been investigated in steam at 973 K for 28 Ms. An FeAl layer with a thickness of 70 &mu;m was observed to form on the alloy surface during aluminizing treatment, which consisted of hot pressing of pure Al foil of 50 &mu;m thickness on to the sheet specimens at 523 K, and subsequent diffusion annealing at 1373 K for 3.6 ks in vacuum of 10^-4 Pa. The sheet specimens subjected to the aluminizing treatment exhibit excellent oxidation resistance in steam at 973 K, resulting from the formation of very thin Al₂O₃ scale. Oxidation tests were carried out using specimens with a thin layer of FeAl, and specimens with no FeAl layer but different Al concentrations at the alloy surface. Excellent oxidation resistance was observed due to Al₂O₃ scale formation when the FeAl layer was present or the Al concentration at the alloy surface with no FeAl layer was higher than 11%. When the Al concentration at the alloy surface with no FeAl layer decreased below 11%, thick scale of Fe₃O₄ and Fe₂O₃ formed during oxidation.<br>