Mg-doped Ce0.5Zr0.5O2 nanocrystalline powders were prepared via hydrothermal method through homogeneous nucleation at 453K followed by calcinations at 673K. The effect of Mg-doping concentrations on the structure and performances of Ce0.5Zr0.5O2 was studied. The results showed that Mg-doped Ce0.5Zr0.5O2 was a single fluorite-type phase and the size was about 4nm. The introduction Mg into the Ce0.5Zr0.5O2 lattice limited the mobility of oxygen and made the specific surface area and oxygen storage capacity(OSC) declined at doping constant less than 4mol%; as more than 4mol%, a segregation of Mg was dispersed on surface of Ce0.5Zr0.5O2 and improved the thermal stability of surface, thus enhanced the OSC performance.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.