The fractal characteristics of nano-sized powders of CeO 2 -YO 1 . 5 solid solutions, prepared by combustion synthesis and calcined at various temperatures, have been investigated by small angle X-ray scattering technique. Results show a mass-fractal behavior for the powders with mass-fractal dimension D m in the range 2.2-2.6. The estimated particle radii are in the range of 4-15nm, which is in close agreement with TEM results. For the powders calcined at higher temperatures, the particle interface has a tendency to become rough with a significant growth in the particle size and polydispersity.