Porous materials silica aerogels and xerogels were obtained through a sol-gel process from TEOS. Samples derived from different preparation circumstances were investigated via small-angle X-ray scattering. The power-law dependence of the scattered intensity, a characteristic of fractal structures, was observed for all the one-step aerogels. While for the xerogels and aerogels derived from a two-step sol-gel process, the power-law dependence of the scattered intensity was not observed. The xerogels are found to consist of a number of large spherical particles which were densely packed together.