The photoelectrochemical properties of Co‐doped polycrystalline electrodes and undoped electrodes have been investigated. The undoped polycrystalline electrodes heated at temperatures over 700°C give the visible light response in addition to the original bandgap photoresponse. The electrodes prepared at also give the apparent visible light response , when the Co was highly doped in the layer from the surface to the interface of the Ti layer. The visible light response will be based on the newly formed d‐band by the interaction of the interstitial Ti or Co ion in the lattice, which is below the π* conduction band of the in energy position.