X-ray diffraction structural characterization of heterogeneous catalysts, which are typical nanomaterials, requires development of special methods taking into account the X-ray scattering from small objects. Data on the development of an X-ray diffraction method of radial electron density distribution (REDD), or pair distribution function method (PDF analysis), based on the integrated analysis of X-ray scattering are presented. This  method gives information on interatomic distances and coordination numbers and is primarily used to detect and evaluate the size of nanoassociates (phases) < 3 nm, which are not detected by the conventional powder X-ray diffraction analysis of interplanar distances. Being sensitive to changes in the local structure in the length range of 1-3 unit cells, the method can be successfully applied to detect defects in the local atomic structure of nano-objects. Examples of the application of this method for structural studies of nanosized supports and supported catalysts are presented.