NiO/YSZ composite powders, with various NiO contents, have been prepared by the urea hydrolysis method. The crystallization behavior and microstructure of composite powders has been studied in detail. using differential scanning calorimetry analysis, X-ray diffraction, and transmission electron microscope. The results indicated that the actual NiO content of the NiO/YSZ powders largely deviated from the nominal value, and finally reached a saturated value. The NiO addition would retard the crystallization of NiO/YSZ composite. When the calcination temperature was increased, the NiO crystallites first precipitated at around 500 degrees C, and then the YSZ phase presented at about 600 degrees C. The calcined powders consist of NiO/YSZ nanocomposite particles, which are comprised of nano-sized NiO and YSZ crystals. In addition, with the aid of H-2 plasma treatment, it is easier to distinguish the Ni and YSZ phases of Ni/YSZ cermets after sintering and subsequent reduction. This could reveal that such Ni/YSZ cermets exhibited a uniform microstructure that has fine Ni particles homogeneously dispersed within the YSZ matrix. As the NiO content was increased, the size and density number of the Ni phase within an YSZ matrix was increased. (C) 2009 Elsevier B.V. All rights reserved.