Aluminum nitride (AlN) possesses excellent physical properties such as low thermal expansion coefficient and high thermal conductivity and electrical resistivity. In spite of large application in refractory industry, this material tends to be oxidized at high temperature in the environmental atmosphere which affects on its long-term service. Study of oxidation behavior of this material is therefore of high importance from both fundamental and application point of view. In the current research, the oxidation kinetic of AlN powder was explored by means of thermogravimetry. Nonisothermal tests results showed that oxidation of nano-scale powders starts from lower temperatures in compare of micro-scale ones. Using iso-thermal data, the oxidation kinetic was discussed by means of corresponded equations and controlling mechanism was identified consequently. To elaborate the oxidation kinetic, the process was divided by two parts; using the first-order equation (nucleation and growth mechanism) in the initial stages following by Jander equation for diffusion mechanism. Activation energy was calculated in either steps showing reasonable consistency with the literature. The effect of temperature on oxidation kinetic of micro-scale powder and effect of reduction in particle size (for a same temperature) was shown by mathematical equation in each step.