Nanocrystalline thoria-ceria (Th1-xCex)O-y powders in a ratio of x = 0.05-0.5 mol% were prepared by a co-precipitation process, which employs thorium and cerium nitrate as thorium and cerium source material, deionized water as solvent and ammonia gas as precipitant. Cerium was used as a simulator for plutonium and the other actinides with a +4 valency. After co-precipitation the aqueous (Th1-x,Ce-x,)(OH)(y) center dot nH(2)O cakes had been dried at 110 degrees C, these powders were separately milled in acetone, carbon tetrachloride, n-dodecane, isopropanol and water before and/or after calcination at different temperatures (300-600 degrees C). DTA-TG, XRD, TEM and BET analyses were performed to characterize the produced powders. Characterization results revealed that the materials were not crystallized, even the temperature reached up to 600 degrees C. The crystallization of (Th1-xCex)O-y began at about 600 degrees C. The crystal growth took place between the temperatures 600 degrees C and 1200 degrees C. The powders have a range average crystallite sizes from 5 to 115 nm, with a specific surface area from 6 to 111 m(2)/g depending on the calcination temperature and Cc mol%. In this way the crystallized nano (Th1-xCex)O-2 powder with a higher specific surface area is able to be produced to obtain the pellets in very high density. (c) 2007 Elsevier B.V. All rights reserved.