Well-size-distributed nanopowders of lanthana-yttria-zirconia ternary oxide were synthesized by hydrothermal method. The effects of La2O3 on crystal growth and phase transition of YSZ nanocrystallite were investigated in detail with 8La(2)O(3)-8YSZ as an example. X-ray Diffraction (XRD), Thermogravimetric analysis (TG) and Differential Scanning Calorimeter analysis (DSC), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) were applied to characterize the phase formation, thermal decomposition and morphology of nanopowders. The XRD results indicate that 8La(2)O(3)-8YSZ is composed of both the face-centered cubic (ZrO2) and pyrochlore (La2Zr2O7, LZ) structures. The average crystallite size obtained from TEM observation is 5-7 nm. The sample has a specific surface area of 201.2 m(2) g(-1), which is obviously higher than that of 8YSZ (145.9 m(2) g(-1)). Moreover, the effective activation energy (Q) of crystal growth of 8La(2)O(3)-8YSZ and 8YSZ can be divided into two stages: below 900 degrees C, Q(8YSZ) = 5.68 kJ mol(-1) and Q(8La2O3-8YSZ) = 1.91 kJ mol(-1); in the range of 900-1300 degrees C, Q(8YSZ) = 53.2 kJ mol(-1) and Q(8La2O3-8YSZ) = 81.2 kJ mol(-1). Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.