A doubly N-confused hexaphyrin dinuclear cobalt complex (Co2DNCH) is revealed as an efficient water oxidation catalyst, outperforming the mononuclear cobalt porphyrin with the same aryl group as those in Co2DNCH. By photoirradiation of a water/acetone-d6 (9:1) mixture containing Co2DNCH, [RuII(bpy)3]2+, and S2O82- as the water oxidation catalyst, photosensitizer, and sacrificial electron acceptor, respectively, with visible light, O2 was obtained as the maximum with turnover number = 1200, turnover frequency = 3.9 s-1, and quantum yield = 0.30.