Oxidation behavior of MoSi2 was investigated in air over the temperature range of 1400-1700 A degrees C. Spallation of the SiO2 scale did not occur at any temperature, and Mo5Si3 formation did not happen below 1700 A degrees C. A change in the rate-controlling mechanism was detected within the temperature range of this study. Activation energy for oxidation of MoSi2 at high temperatures was determined to be 204 kJ/mol. This value is less than the value of activation energy for oxidation of MoSi2 controlled by diffusion of O-2 through amorphous SiO2 layer reported at lower temperatures. The decrease in activation energy is attributed to the increased degree of crystallization of amorphous silica to beta-cristobalite at high temperatures resulting in enhanced O-2 diffusion through SiO (4) (-4) tetrahedral structure.