In the present work, a nanostructured Zr0 5Ce0 5O2 solid solution was synthesized using a citrate complexatton technique with different thermal treatments. The resulting powders were characterized by employing X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) A qualitative analysis of the XRD data indicated that all samples exhibited a tetragonal phase (P4(2)/nmc space group). In HRTEM observations, the internal crystal structure of the nanoparticles was studied and the primary particle sizes were measured Average crystallite size, obtained from the XRD data using the Scherrer equation, ranged from 4.1 nm to 7 7 nm (C) 2009 Elsevier B.V. All rights reserved.