The development of a highly active manganese-based water oxidation catalyst in the design of an ideal artificial photosynthetic device operating under neutral pH conditions remains a great challenge, due to the instability of pivotal Mn3+ intermediates. We developed defective and “c-disordered” layered manganese oxides (MnOx-300) formed on a fluorine-doped tin oxide electrode by constant anodic potential deposition and subsequent annealing, with a catalytic onset (0.25 mA/cm2) at an overpotential (η) of 280 mV and a benchmark catalytic current density of 1.0 mA/cm2 at an overpotential (η) of 330 mV under neutral pH (1 M potassium phosphate). Insightful studies showed that the main contributing factors for the observed high activity of MnOx-300 are (i) a defective and randomly stacked layered structure, (ii) an increased degree of Jahn–Teller distorted Mn3+ in the MnO6 octahedral sheets, (iii) effective stabilization of Mn3+. These results demonstrate that manganese oxides as structural and functional models of an oxygen-evolving complex (OEC) in photosystem II are promising catalysts for water oxidation in addition to Ni/Co-based oxides/hydroxides. However, catalytic active site and catalytic mechanism is not realed on molecular level. We recently obtained detailed structural information about the active site by the XAS analysis. It is a chance to propose several reasonable structure of active site and to further conduct the mechansim study on this super active MnOx catalyst by DFT caculations.