A series of photocatalysts, BiTa(1-x)Cu(x)O(4) (x = 0.00-0.04), were synthesized by the conventional solid-state reaction method and their electronic structures and photocatalytic activities were investigated. The electron microscope observations revealed that the particle sizes of BiTaO(4):Cu crystals were smaller and the surface with many characteristic steps was more obvious than that of the nondoped BiTaO(4), which lead to the increase of photocatalytic activity of water splitting. The UV-vis spectra indicate that the Cu(2+) ions doping not only enhanced the photocatalytic activity under ultraviolet-visible (lambda > 300 nm) light irradiation but also induced the visible light (X > 400 nm) response. The photocatalyst doped with 2 mol% Cu(2+) and loaded with 0.3 wt% RuO(2) co-catalyst was found to have the highest activity. New band gap in the visible light range is obtained by copper-doped BiTaO(4), which is attributed to the transition from the donor level resulting from the Cu impurity to the conduction band of BiTaO(4) doped with copper on the basis of the result of DFT calculation. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.