Perovskite oxides, CaTi1-xCuxO3, with the density of copper ions, x, ranging from 0.01 to 0.04, were prepared by sol-gel method coupled with ultrasonic technique for the first time. The determination by X-ray diffraction pattern of crystal structure and UV-visible light adsorption studied by ultraviolet-visible absorption spectroscopy (UV-vis) were reported. Electronic structures were investigated by density functional theory (DFT). It has been found that CaTiO3-doped with 2 mol% Cu2+ exhibits the highest activity to the photocatalytic decomposition of water. Photocatalytic activity of doped CaTiO3 powder for hydrogen evolution under UV light is increased dramatically about 8 times than that of pure CaTiO3 powder when the NiOx is used for cocatalyst. The results of DFT calculation illuminate that absorption of visible light is mainly due to the transition from the donor levels formed by Cu2+ to the conduction band of copper-doped CaTiO3. (C) 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu.