A nanoporous amorphous manganese oxide is investigated as electrocatalyst for the oxygen reduction reaction in alkaline solutions. Cyclic voltammetry of catalytic electrodes based on the amorphous manganese oxide in oxygen-saturated electrolytes indicates that the amorphous manganese oxide catalyzes a two-electron reduction of molecular oxygen to HO 2 −. An oxygen reduction current density of more than 100 mA/ cm 2 is attained with an oxygen back-feed gas diffusion electrode with a low-catalyst loading of ca. 0.85 mg/ cm 2 . The significant catalytic activity might be due to high concentration of lattice defects and active sites of the amorphous material, which would have potential applications in metal–air batteries and low-power fuel cells.