The phase transition and morphology of spherical γ-Al2O3 powder were studied by using alumina nitrate as the starting material. Aqueous Al2O3 sols (pH 3) were prepared at different preparation temperatures, such as 80 and 95℃. As each sol of pH 3 went through the aging process, its pH was readjusted to pH 9 and 10 by adding triethylamine and ammonia water, respectively. The aging times were 10 and 50 h for pH 9 and time when the sol was prepared at 80℃ and ammonia water was used during the aging process. However, from the results of XRD analysis, the extent of the phase transition from the Al2O3 precursor aged at pH 10 to γ-Al2O3 powder was higher than that aged at pH 9. The shapes of all the γ-Al2O3 powders obtained through out this study of the phase transition were amorphous. The morphology control of amorphous γ-Al2O3 powder was achieved by employing a W/O emulsion method.