Photocatalytic H-2 formation from aqueous glycerin was achieved over giant polyoxometalate complexes Na21K4[{P2W15Ti3O57.5(OH)(3)}(4)Cl]center dot 104H(2)O and Na18H15[{P2W15Ti3O59(OH)(3)}(4){mu(3)-Ti(OH)(3)}(4)Cl]center dot 105H(2)O to develop a new application for glycerin, an oversupplied compound accompanying biodiesel production. This is the first example of the catalytic formation of H2 by use of a photocatalyst and glycerin and is also the first example of a photochemical application of giant polyoxometalate complexes. The catalytic reactions proceed at room temperature under irradiation with UV-visible light without the use of any cocatalyst. The reaction mechanism can be explained by redox reactions between the complexes, water, and glycerin.