A simple method is described to prepare submicrometer alpha-alumina by burning carbon supported on the surface of gamma-alumina in oxygen flow at a temperature of 800 degrees C. The burning of carbon generates a large amount of heat and leads to a rapid increase in the local temperature inside the pores of alumina. When the temperature is high enough for the phase transformation, alpha-alumina is obtained in a very short time. It was found that, for carbon contents between 6 and 10 wt%, all the gamma-alumina could transform into alpha-alumina after burning of carbon in oxygen for a short time, and the transformed particle sizes of alpha-alumina were mostly no more than 1 mu m.