This paper reports the results of an investigation aiming at finding what affects the grain size of namo-TiO2 powder during synthesis. Nano-sized TiO2 powders have been prepared by a sol-gel method. The crystalline structures and morphologies of the powder have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The result shows that the different preparation conditions such as concentration, pH value, calcination time and calcination temperature have a lot of influences upon the properties of nano-TiO2 powders. The smallest grain size of TiO2 powder we have obtained is 6 nm by controlling the process conditions. (C) 2002 Elsevier Science B.V. All rights reserved.