Catalysts prepared from the carbon black impregnated with manganous nitrate solution and then heated at temperature from 270 degreesC to 450 degreesC were investigated. It was found that the impregnated catalysts heated at temperature of 340 degreesC 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 degreesC were different from those below 340 degreesC. The enhanced catalysis of air electrodes was ascribed to the formation of MnO2 crystal with d-value of 2.72 Angstrom as the impregnated-catalysts was heated at temperature of 340 degreesC. The other factors in preparation of air electrodes were also discussed.