Aluminum ammonium sulfate (AA) solution (0.1 mol/l) and ammonium hydrogen carbonate (AHC) solution (1.2 mol/l) were allowed to react at room temperature. The precipitates formed were kept with the mother liquor in a closed vessel and aged at 100 °C. Acicular-shaped crystalline particles of Al(NH4)CO3(OH)2, (AACH), were obtained after the elongated aging period. Acicular α-alumina particles were obtained through the thermal decomposition at 1300 °C out of the AACH particles which were previously treated with a small amount of tetraethoxysilane (about 1.6 wt. % of SiO2).