Thermal decomposition of aluminum isopropoxide (AIP) in inert organic solvents ( toluene and mineral oil) resulted in the formation of chi-alumina. Phase evolution by calcination at various temperatures for this alumina was studied via X-ray diffraction. The results suggest a direct transformation from chi-alumina to alpha-alumina at approximately 1180degreesC, without the formation of kappa-alumina phase, while still maintaining the small particle size (< 100 nm). The transformation behavior was observed by TEM and the crytallite size was calculated by the Scherrer equation. The results indicate one χ-alumina crystal transforms into one α-alumina crystal at its critical size in a nucleation step. This crystal exhibits a rapid grain growth following the transformation. (C) 2004 Kluwer Academic Publishers.