Mesoporous transition alumina was prepared by spray pyrolysis of an alumisol precursor, without the use of structure-directing reagents. The prepared alumina exhibited a well-defined mesoporous structure with narrow pore size distribution (3.0-4.7 nm). Preparation temperature played a major role in the phase formation and the porosity of prepared alumina. The phase transformation of boehmite to gamma-Al2O3 and theta-Al2O3 was observed at 800 and 1200 degrees C, respectively. An increase in preparation temperature resulted in a decrease in surface area and pore volume and an increase in pore size. Longer residence time promoted the crystallinity of prepared alumina effectively, but it also led to the formation of particles with smaller surface area, lower pore volume, larger pore size, and broader pore size distribution. Additionally, while alumisol concentration had little effect on the surface area, its reduction led to a decrease in pore volume and pore size and caused the formation of bimodal pore size distribution. The as-prepared alumina also exhibited excellent thermal stability, showing great application potential for industry. (C) 2010 Elsevier B.V. All rights reserved.