Weakly agglomerated nanocrystalline YSZ (yttria-stabilized zirconia) was synthesized by three different routes, namely homogeneous precipitation, ammonium hydroxide-based directly hydrothermal and urea-based homogeneously hydrothermal methods. The XRD and TEM results showed that well-crystallized nanocrystalline YSZ with homogenous and weakly agglomerated assembly was obtained from these processes. The Raman scattering results of the three samples suggested that cubic zirconia was formed as major phase, and consisted of the tetragonal zirconia as minor one. The sintering behavior of the two hydrothermal samples indicated a significant shrinkage at T < 570 degrees C. However, the shrinkage rates of the three samples showed similar at T > 570 degrees C. Impedance spectroscopy was used to determine the ac ionic conductivity. The total and grain boundary conductivities of the sample obtained from ammonium hydroxide-based hydrothermal method were higher than those of the samples obtained from homogeneous precipitation and urea-based homogeneously hydrothermal methods, whereas the total and grain boundary activation energies of the former being slightly lower. (C) 2006 Elsevier Ltd. All rights reserved.