The kinetics of oxidation of manganese have been studied in mixtures at temperatures of 800°–1200°C. In most cases the oxidation was parabolic. Activation energies for parabolic oxidation in different gas mixtures were found to range from 40.5 to 45.6 kcal/mole. In a few cases where manganese specimens were oxidized below 1000°C in gas mixtures with a high content of carbon monoxide, weight gains were abnormally large and the parabolic rate law was not obeyed. In these cases carbon deposits were formed on the oxide, and cracks of the scale were observed. Marker studies revealed that manganous oxide grows by the outward migration of manganous ions. From the oxidation data, the self‐diffusion coefficient of manganous ions is determined as a function of , and the mechanism of oxidation is discussed.