Abstract: A method for manufacturing a Ni-based alloy article which elutes little Ni even when used in a high-temperature water environment for a long period comprises heating the Ni-based alloy in a carbon dioxide-containing atmosphere for a set period of time at an elevated temperature to form an oxide film comprising chromium oxide on a surface thereof. Using carbon dioxide as an oxidizing gas produces an oxide film of generally uniform thickness along a length of the article being treated so that resistance to nickel elution is more uniform over the entire article.