A study was conducted to show that up to 4.5 mol% nitrogen can be introduced into ceria under reducing conditions between 550 and 900 °C through ammonolysis. Powder samples of CeO2 were treated in flowing NH3at a rate of 270 cm3/min and temperatures between 400 and 1100°C during 17 hour and were subsequently quenched to room temperature in the ammonia atmosphere. The Ce ions content show that cerium is reduced from above 650°C but the amount of ions increase significantly above 750°C. All of the CeO2 samples obtained up to 780°C are found to contain a single cubic phase by power X-ray Diffraction analysis. The 400.1 eV of binding energy corresponds to molecularly chemisorbed nitrogen at the ceria surface, while 397.4 eV contribution is assigned to the formation of Ce-N bonds.