To provide a visible light responsible Ti oxide film which has hydrophilicity and antifogging property and is excellent in transparency and which has an ability to decompose gas by UV radiation, and a process for its production, as well as a Ti oxide film-coated substrate. A Ti oxide film formed on a substrate, characterized in that when a voltage is applied to the Ti oxide film while the Ti oxide film is irradiated with light of a xenon lamp having a luminance of 100 mW/cm2 and having ultraviolet light of less than 400 nm cutoff, the electric current value is at least 1,000 times the electric current value when the same voltage as said voltage is applied to the Ti oxide film in a dark place.