Photocatalytic V5+ reduction accompanied by O-2 evolution over WO3 is reported for the first time. Water oxidation reaction utilizing VO2+ ion as an electron acceptor proceeded photocatalytically over WO3. The activity of WO3 was remarkably enhanced by the presence of Fe3+/2+ ion at the ion-exchange site on WO3 surface, and its apparent quantum yield (AQY) was 22% at 420 nm. Moreover, the AQY was raised to about 78% when a small amount of formic acid was added to reactant solution.