Abstract: Cylindrical aluminum ammonium carbonate clusters were successfully prepared from γ-Al2O3 powder and ammonium bicarbonate by hydrothermal method. Al2O3 were also prepared from the cylindrical aluminum ammonium carbonate cluster precursor. The effects of reaction temperature, reaction time and material ratio on the morphology of cylindrical aluminum ammonium carbonate clusters and the phase transformation process and the properties of γ-Al2O3 were investigated by XRD, SEM, N2 adsorption-desorption and TEM. The results showed that the optimum reaction conditions were as following: the mass ratio of γ-Al2O3 powder to ammonium bicarbonate of 1:1.75, the reaction temperature 140 ℃, and the reaction time 6 h. The diameter of the synthesized cylindrical aluminum ammonium carbonate clusters was 5-15 μm. The cylindrical aluminum ammonium carbonate cluster was formed by cross-stacking of cylindrical aluminum ammonium carbonate with a diameter of 50-100 nm and a length of 0.5-3 μm. When the calcination temperatures were 600, 800, 1 000，1 300 ℃, aluminum ammonium carbonate clusters were successively transformed to γ，η，α aluminum. The specific surface area of the γ-Al2O3 was 300 m2/g, pore volume was 0.67 mL/g, and more than 50% of the total pore volume was over 15 nm in diameter.

Key words: aluminum ammonium carbonate, cluster, synthesis, hydrothermal treatment, phase transition