Simple transition metal oxides such as NiO, Co3O4, Fe3O4 and Cu2O were found to catalytically decompose water into H-2 and O-2 by mechanical energy, The reaction is regarded as "mechano-catalytic'' overall water splitting" and is a quite novel catalytic reaction. In this paper, some,general aspects on the mechano-catalytic overall water splitting are reviewed on simple oxides. In addition, recent results on the mechano-catalytic activity of a groups of mixed oxides, wolramite-type oxides with a formula of ABO(4) (A = Fe, Co, Ni and Cu, etc., B = W, Mo), are shown. AWO(4) (A = Fe, Co, Ni and Cu) decomposed water into H-2 and O-2 under the supply of mechanical energy, indicating that mechano-catalytic overall water splitting proceeded on wolframite-type compounds containing 3d-transition metals. AMoO(4) (A = Fe, Co, Ni) also decomposed water into H-2 and O-2 under supply of mechanical energy. The reaction properties on wolframite-type oxides are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.