Titanium dioxide nanotubes are synthesized using sol-gel method. Electron energy-loss spectroscopy has been used to investigate the chemical composition of the nanotubes. The results show that the atomic ratio of O/Ti is very close to two. Electron diffraction studies indicate that the nanotubes have the anatase structure. High-resolution transmission electron microscopy studies show that the nanotubes possess a layered structure with layer spacing of about 7.1 Angstrom. The tube axis is determined to be along [010] direction of the anatase phase. The formation mechanism of the nanotubes can be explained as 3D --> 2D --> 1D. The two-dimensional lamellar TiO2 is essential for the formation of the nanotubes. (C) 2002 Elsevier Science B.V. All rights reserved.