The photocatalytic properties of gallium oxides that were prepared by precipitation methods to the overall splitting of H2O were studied. The photocatalytic behavior of the NiO-loaded gallium oxides to this reaction could be separated into three categories on the basis of the preparation temperatures of the gallium oxides. The photocatalytic behavior of each category reflected the behavior of corresponding crystal phase of gallium oxides. Of these categories, NiO-loaded alpha-Ga2O3, which composed the second category, exhibited remarkably high photocatalytic activity compared with those of NiO-loaded GaO(OH) and NiO-loaded beta-Ga2O3 which composed the first and third categories, respectively. Through investigations, such as the characterization of the prepared gallium oxides, the effects of combining RhyCr2-yO3 co-catalyst with the photocatalytic activity and the effects of the preparation methods on the photocatalytic reaction, the influences of the states and the morphologies of the gallium oxide photocatalysts to the photocatalytic overall splitting of H2O were discussed. (C) 2013 Elsevier Inc. All rights reserved.