Single-crystalline ceria nanorods were fabricated using a hydrothermal process and annealed at 325 °C-800 °C. As-synthesized CeO2 nanorods contain a high concentration of defects, such as oxygen vacancies and high lattice strains. Annealing resulted in an improved lattice crystalline quality along with the evolution of novel cavity-shaped defects in the nanorods with polyhedral morphologies and bound by e.g. {111} and {100} (internal) surfaces, confirmed for both air (ex situ) and vacuum (in situ) heating. We postulate that the cavities evolve via agglomeration of vacancies within the as-synthesized nanorods.