Lead tungstate, PbWO4, with a tetragonal structure was found to make a stable photocatalyst for the decomposition of water to produce H-2 and O-2 when combined with RuO2. This is the first example of tungsten oxide that is photocatalytically active for the reaction. The structural feature of PbWO4 is the presence of tetrahedral WO4. The DFT calculation showed that Ph2+ with d(10)s(2) electronic configuration had significant influences on both valence and conduction band structures.