A method for oxidizing a nitride film is disclosed, which includes the steps of: providing a nitride film formed on an electrically conductive substrate; irradiating the nitride film with a light beam and getting close to the nitride film with a electrically conductive probe; and exerting a bias between the electrically conductive substrate and the electrically conductive probe. The method can oxidize the nitrides quickly and reduce the cost building a nano-structure in the nitride film. An apparatus for oxidizing a nitride film is also disclosed herewith.