Oxygen incorporation into electrolytic manganese dioxide (EMD)-derived manganese oxides has been systematically investigated by x-ray diffraction, chemical analysis, thermal analysis, and temperature programmed desorption tech niques, and compared with MnCO3-derived oxides. It has been found that the stability of Mn3O4 is quite different depending on the EMD starting material and on how it was treated. EMD-derived Mn3O4, can be classified into three types in terms of the behavior of the thermal incorporation of external oxygen. All MnCO3 derivatives and EMD derivatives with a low calcination temperature belong to Mn3O4-Type I, which undergoes oxidation in the temperature range of 570 to 900 degrees C when calcined in air. On the other hand, Type II-Mn2O3 samples calcined at a high temperature are thermally stable alone, but become oxidizable in the presence of EMD Mn2O3. The others belong to Mn3O4-Type III, which is thermally stable regardless of the presence of ENTD.