An object is to provide an inexpensive photocatalyst that can be used for degradation of organic substances or sterilization, can be used in any situations, is highly safe, and absorbs light having a wide range of wavelengths including visible light to exhibit an activity. A photocatalyst including, as an active component, a reaction product obtained by mixing a reducing organic substance having iron-reducing ability or a feedstock for supplying the reducing organic substance with an iron-supplying source in the presence of water is provided； specifically, a photocatalyst in which the reaction product exhibits a photocatalytic activity when irradiated with light having a wavelength of ultraviolet light, visible light, or infrared light； an organic substance degradation method including bringing the photocatalyst into contact with an object to be degraded and irradiating the photocatalyst with light having a wavelength of ultraviolet light, visible light, or infrared light； and a sterilization method including bringing the photocatalyst into contact with an object to be sterilized and irradiating the photocatalyst with light having a wavelength of ultraviolet light, visible light, or infrared light.
