The thermal and structural stability under different atmospheres of a series of CeO2/Al2O3 supports with a range of composition containing 2-25% CeO2 was examined. It is shown that treatment under reducing conditions strongly affects stability in terms of surface area and phase distribution. Under oxidizing conditions at 1473 K, ceria is almost totally ineffective as a stabilizing agent for alumina whereas under reducing and redox conditions, its effects are remarkably enhanced, and surface area in the order of 60 m(2)/g can be retained after treatment at 1473 K for several hours. This is directly related to the formation of Ce3+ present mainly as CeAlO3, which inhibits crystal growth and prevents formation of the oc-alumina responsible for decrease in surface area.