The oxidation kinetics, morphology, and crystallinity of aluminum nitride (AlN) powder thermally oxidized in flowing oxygen were determined from 800 degrees to 1150 degrees C. At 800 degrees C the oxidation became detectable with weight change. AlN powder was almost completely oxidized at 1050 degrees C after only 0.5 h. Amorphous aluminum oxide formed at relatively low temperatures (800 degrees-1000 degrees C), with a linear oxidation rate governed by the oxygen-nitride interfacial reaction. Transmission electron microscopy displayed individual aluminum oxide grains which formed a discontinuous oxide layer at this temperature range. The aluminum oxide was crystalline at higher temperatures (> 1000 degrees C), as detected by X-ray diffraction, and the density of oxide grains increased with temperature.