Abstract: Based on recent developments in the theory and application of small-angle X-ray scattering (SAXS) we summarize our progress in applying SAXS to the structural characterization of materials. These studies involve three research areas, namely, the determination of the electron density fluctuation in organic/inorganic hybrid materials, studies of the chord length distribution in mesoporous sieves, and investigation of the structural evolution of ZrO2 nanoparticles during calcination.