To provide a transparent optical substrate, in which particles of an inorganic metal oxide as a photocatalyst are firmly adhered to the substrate surface so as to suppress peeling of the film, thereby, the substrate surface is protected and scratch resistance of the surface is improved, the photocatalytic effect is activated even with visible light, the coating surface is rendered to hydrophilic in a high level as well as an antistatic effect is improved, and generation of interference fringes of SiO2 is prevented.

The transparent optical substrate has a photocatalytic inorganic metal oxide film comprising at least titanium oxide in a form of fibrous ultrafine particles having an average fiber width and thickness of 1 to 50 nm, an average fiber length of 10 to 1000 nm, an average aspect ratio of 2 to 100, and a specific surface area of 30 m2/g or more. The photocatalyst contains, as inorganic elements in terms of semi-quantitative values, at least Ti by 90 to 97 wt.%, Si by 2.3 to 30 wt.%, Ag by 1.4 to 2.2 wt.% and Zn by 0.2 to 0.3 wt.%, and contains, as organic elements in terms of quantitative values, at least C by 55 to 65 wt.%, H by 8 to 12 wt.% and N by 0.2 to 0.4 wt.%. The photocatalytic inorganic metal oxide film containing titanium oxide fixed to the substrate surface shows a pencil hardness scale of 3H or harder.