Ag+-doped TiO2 films on stainless steel were prepared by a sol-gel method and their microstructures and compositions were studied with X-Ray Diffractometer, Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy. It was shown that Fe atoms in untreated stainless steel react with Ag+ in the TiO2 film and form FeTiO3, which has an acicular crystal form under SEM observation. As a result, Ag+ in the film is reduced to the silver atom, which degrades the antibacterial property of the film. However, after an oxidization of the substrate, a layer of ferric oxide is formed, which reacts with Fe atoms that would otherwise react with and reduce Ag+, and then forms FeTiO3. Thus, the penetration of Fe atoms is stopped and Ag+ in the anatase-structure TiO2 film is protected from the reduction, which enhanced antibacterial property of the film.