A titanium oxide photocatalyst responsive to visible light which can exhibit a high photocatalytic activity in response to visible light is produced by subjecting titanium oxide and/or titanium hydroxide obtained by neutralizing an acidic titanium compound with a nitrogen-containing base to heat treatment in an atmosphere containing a hydrolyzable metal compound (e.g., a titanium halide) and then to additional heat treatment in a gas having a moisture content of 0.5-4.0 volume % at a temperature of 350.degree. C. or above. The photocatalyst which is a nitrogen-containing titanium oxide has no substantial peak at a temperature of 600.degree. C. or above in a mass fragment spectrum obtained by thermal desorption spectroscopy in which the ratio m/e of the mass number m to the electric charged e of ions is 28, and the peak having the smallest half band width is in the range of 400-600.degree. C. in the spectrum. The nitrogen content calculated from the peak appearing at 400 eV.+-.1.0 eV in the N1s shell bonding energy spectrum obtained by XPS measurement of this photocatalyst is at least 20 times larger than the nitrogen content obtained by chemical analysis.