In the present study, we synthesized boehmite (gamma-AlO(OH)) fine particles hydrothermally at 350 degrees C and 400 degrees C using a flow reaction system. The influences of the synthetic parameters including temperature, pressure, starting Al(NO3)(3) concentration, and pH of the starting solution, on the boehmite particle size were investigated. Products were characterized by X-ray diffractometry and transmission electron microscopy. According to XRD analyses, all the product were crystalline gamma-AlO(OH). From the results of TEM observation, the morphology of gamma-AlO(OH) particles obtained was rhombic or hexagonal plates with 70-470 nm of the average particle size. The particle size increased with an increase in the reaction temperature and the starting Al(NO3)(3) concentration, while that decreased with an increase in the pH of the starting solution. Moreover, at 400 degrees C the particle size enlarged from 170 nm to 300 nm with increasing reaction pressure from 25 MPa to 40 MPa, while there is no dependency of reaction pressure on the particle size at 350 degrees C. Furthermore, the particle formation and growth mechanisms are discussed based on the solubility of gamma-AlO(OH) under hydrothermal conditions. (c) 2005 Elsevier B.V. All rights reserved.