Aluminum chloride (AlCl3) was evaporated and partially hydrolyzed in water vapor at 300-700 degrees C in a tubular reactor, 2.4 cm in diameter and 50 cm in length, to form alumina-precursor particles that were more spherical and less agglomerated compared with the fumed alumina produced by flame hydrolysis and oxidation. This study was focused on the effects of the H2O to AlCl3 molar ratio, the reactor temperature, the AlCl3 concentration, and the contact point of AlCl3 with H2O vapors on the morphology, size, and chemical composition of the obtained particles. The primary particle size ranged from 50 to 200 nm depending upon the operating conditions. The particle size increased with increasing AlCl3 concentration but decreased with increasing reactor temperature or with increasing molar ratio of H2O to AlCl3. The particle size became smaller and the particle size distribution narrower as the contact point of AlCl3 with H2O vapors was moved from the inlet of the reactor to a point 10 cm inward toward the center of the reactor. The primary particle sizes were simulated with a discrete-sectional model under different operating conditions. The as-produced particles contained chlorine because of the incomplete hydrolysis; the atomic ratio of Cl to Al in the resulting particles was measured to be 0.21-0.47 or 10-15% of the chlorine in the AlCl3 charged for the hydrolysis. The particles prepared at the reactor temperature of 500 degrees C were calcined at 1200 degrees C for 1 h. The calcined particles were chlorine free, alpha in crystalline phase, 98 nm in surface-area equivalent diameter, and 0.81 g/cm(3) in bulk density.