Nano-Ce1-xZrxO2 (x = 0.15, 0.25, 0.5) were synthesized via co-precipitation using NH4OH as precipitant and hydrothermal crystallization. The XRD results confirmed that the cubic fluorite nano-Ce1-xZrxO2 can form in NH4OH solution (pH > 10) at 150 degrees C for 12 h, and well crystallized 20-50 nm nano-Ce1-xZrxO2 were obtained at 200 degrees C for 22 h. The crystal growth of Ce1-xZrxO2 was suppressed under higher OH- concentration and crystallite size decreased with increasing concentration of NH4OH. Ce3d XP spectra showed that the main valence state of the cerium on Ce1-xZrxO2 surface is +4, and substituting Ce4+ with Zr4+ has no obvious influence on Ce3+/Ce4+ ratio. C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.