Uniform-sized cerium dioxide nanoparticles, nanocubes, and nanorods were synthesized by an inexpensive microwave-assisted method. The shape of cerium oxide nanomaterials could be controlled simply by varying the irradiation time. UV-vis spectrum measurements at various reaction times were used to test the UV absorption ability of nanostructured CeO2 and track the morphological evolution. The results illustrated that the absorption peaks would shift to the higher wavelength when the CeO2 nanocrystals grew from nanoparticles to nanorods. The bandgaps of CeO2 nanomaterials depended on the morphology of nano-CeO2. Based on the observation of shapes and sizes of CeO2 nanocrystals at different irradiation times and calculation from XRD patterns, a possible growth mechanism of CeO2 nanorods was put forward to explain the experimental observations. (C) 2010 Elsevier B.V. All rights reserved.