Nano-sized domains have been widely observed in rare-earth-doped ceria, but their structure model remains unclear. In this work, based on the study of high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) of Gd-doped ceria, the structure model of the domains was constructed by a combination of defect clusters with oxygen vacancy chains. Then, the SAED patterns were simulated using this structure model. The simulated results are consistent with the observed SAED patterns. (C) 2009 Elsevier B.V. All rights reserved.