Catalysts prepared from the carbon black impregnated with manganous nitrate solution and then heated at temperature from 270°C to 450°C were investigated. It was found that the impregnated catalysts heated at temperature of 340°C exhibited the best catalytic activity for oxygen reduction in alkaline electrolyte. It was also found that the XRD spectra of pyrolytic MnO2 from manganous nitrate over 340°C were different from those below 340°C. The enhanced catalysis of air electrodes was ascribed to the formation of MnO2 crystal with d-value of 2.72 Å as the impregnated-catalysts was heated at temperature of 340°C. The other factors in preparation of air electrodes were also discussed.