Nonprecious metal catalysts for oxygen reduction were prepared by heat-treating transition metal (Mn, Fe, Co, Ni, Cu, and Zn) hexacyanoferrate precursors (Prussian blue analogs) dispersed on carbon black under a nitrogen atmosphere. Polarization measurements for oxygen reduction on the prepared catalysts were carried out with a gas-diffusion electrode floating on the surface of alkaline solution under a stream of oxygen. The catalytic activity toward decomposition of peroxide generated during oxygen reduction at the gas-diffusion electrode was examined in situ by monitoring the open-circuit potential recovery after interruption of steady-state cathodic current. The catalytic activity for oxygen reduction on the carbon-based electrode was well correlated with the activity toward peroxide decomposition. A linear relation between the electrode potential at constant current and the logarithm of the peroxide decomposition rate constant was observed. Among the catalysts consisting of several combinations of 3d transition elements, the catalysts containing cobalt or copper with iron exhibited high operation potential of the electrode, and the catalysts containing copper or zinc with iron exhibited high activity toward peroxide decomposition. When the normalized rate constants toward peroxide decomposition were compared with those reported for the conventional catalyst such as transition metal oxides, the catalytic activity of the present catalysts was comparable to or higher than the conventional catalysts. From these results, the possibility of cost-effective catalysts for air cathodes in alkaline solution is discussed. (c) 2007 The Electrochemical Society.