Hydroxides of transition metals cations like Fe(III), Co(III), Mn(III), Ru(IV), etc., appear to be efficient artificial catalysts in oxidation of water to O-2. The paper describes some catalytic properties of these hydroxides. The hydroxide-based catalysts for the water oxidation can be obtained in three modifications: bulky (individual and binary), supported on the ion exchange resins or conventional oxide supports (SiO2, TiO2, Al2O3, zeolites), and colloidal catalysts stabilized by starch. The possible mechanism of the catalytic reaction, including the stage of the formation of peroxocomplexes as intermediates is under discussion. Some similarities are drawn between the catalytic properties of hydroxide catalysts and those of the manganese-based oxygen evolving complex of the Photosystem II of green planes. (C) 2000 Elsevier Science B.V. All rights reserved.