Indium tin oxide (ITO) thin film as one of promising transparent conducting oxide (TCO) films has attracted ever increasing attention owing to its special optical, photocatalytic and optoelectronic properties. In this research, ITO films were prepared by sol-gel dip-coating method and annealed at different temperatures subsequently. The lateral and surface structures of ITO films as well as the structural evolution have been assessed by grazing incidence small angle X-ray scattering (GISAXS) technique. The films show pore fractal structure when annealed at low temperature (<= 800 degrees C) which transforms to a hierarchical fractal structure at high temperature (1000 degrees C). As the temperature rises, films are densified due to the elimination of small pores on the surface at low temperature and the shrinkage of big pores buried inside at high temperature. However, the surface roughness and porosity near the surface are improved at high annealing temperature. (c) 2009 Elsevier B.V. All rights reserved.