Catalysts prepared from the carbon black impregnated with manganous nitrate solution and then heated at temperature from 270℃ to 450℃ were investigated. It was found that the impregnated catalysts heated at temperature of 340℃ exhibited the best catalytic activity for oxygen reduction in alkaline electrolyte. It was also found that the XRD spectra of pyrolytic MnO from manganous nitrate over 2340℃ were different from those below 340℃. The enhanced catalysis of air electrodes was ascribed to the formation of MnO crystal 2 with d-value of 2.72 A as the impregnated-catalysts was heated at temperature of 340℃. The other factors in preparation of air electrodes were also discussed.