Cobalt-containing metal oxides [perovskites (LaCoO 3, NdCoO 3, YCoO 3, La 0.7Sr 0.3CoO 3), spinel (Co 3O 4) and wolframite (CoWO 4)] have been examined as catalysts for photocatalytic water oxidation with Na 2S 2O 8 and [Ru(bpy) 3] 2+ as an electron acceptor and a photosensitizer, respectively. Catalysts with the perovskite structure exhibited higher catalytic activity as compared with the catalysts with the spinel and wolframite structures. LaCoO 3, which stabilizes Co(iii) species in the perovskite structure, exhibited the highest catalytic activity in the photocatalytic water oxidation compared with CoWO 4, Co 3O 4 and La 0.7Sr 0.3CoO 3 which contain Co(ii) or Co(iv) species in the matrices. The high catalytic reactivity of LaCoO 3 possessing perovskite structure was maintained in NdCoO 3 and YCoO 3 which exclusively contain Co(iii) species. Thus, the catalytic activity of Co ions can be controlled by the additional metal ions, which leads to development of highly reactive and robust catalysts for the photocatalytic water oxidation.