Simple transition metal oxides such as NiO, Co 3 O 4 , Fe 3 O 4 and Cu 2 O 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.