Photocatalytic water splitting over La-doped NaTaO3 (NaTaO3:La) was improved by loading with Au cocatalyst which works as H-2 evolution sites. NaTaO3:La loaded with Au by an impregnation method showed higher and more steady activity for water splitting than that by a photodeposition method. This difference in the activity for water splitting was related to the O-2 photoreduction on the loaded Au cocatalyst, which is one of the backward reactions of water splitting. The impregnated spherical Au cocatalyst suppressed the O-2 photoreduction by photogenerated electrons more efficiently than the photodeposited hemispherical Au cocatalyst, because the perimeter of Au/NaTaO3:La interface which produces activated O-2 molecules was smaller in the impregnated Au than the photodeposited Au. (C) 2013 Elsevier B.V. All rights reserved.