YSZ nanocrystals were synthesized by sol-gel method in basic condition (pH = 10). Then, they were modified by sulfate ions using the sulfating agent of sulfuric acid (H2SO4 0.5 M). The synthesized samples showed pure tetragonal phase and the high temperature of 900 degrees C. Modifying Zirconia by both of sulfate ions and yttria significantly increased the stability of tetragonal phase, compared with zirconia modified by either yttria or sulfating ions. XRD, TEM, SEM, FT-IR, and PL analyses have been used to characterize the nanocrystals. All the analyses showed that small size and fairly uniform particles were generated in a range of 10 to 35 nm. (C) 2012 Elsevier B.V. All rights reserved.