Nanosize yttria-stabilized zirconia (YSZ) was synthesized by a novel approach based on molecular decomposition. In this approach, yttria-doped BaZrO 3 (Y+BaZrO 3 ) or yttria-doped Na 2 ZrO 3 (Y+Na 2 ZrO 3 ) precursors were 5rst synthesized from BaCO 3 , ZrO 2 , and Y 2 O 3 or BaCO 3 and commercial YSZ for Y+BaZrO 3 , and from Na 2 CO 3 and YSZ for Y+Na 2 ZrO 3 , by a conventional solid-state reaction method. The precursors were then boiled to leach away the unwanted species, BaO or Na 2 O, either in a dilute HNO 3 solution in water in the case of Y+BaZrO 3 , or in deionized water in the case of Y+Na 2 ZrO 3 . During boiling in HNO 3 or water, the residue of Zr+Y+O skeleton formed 5ne, nanosize YSZ particles. The particle size of the as-synthesized nanosize powders estimated from X-ray diffraction peak broadening was &2+3 nm, while that estimated from speci5c surface area measurements by BET adsorption isotherm was &15 nm. Examination under a transmission electron microscope showed that the crystallite size was &5 nm. Samples were also examined by Raman spectroscopy to determine the crystallographic polymorph of the YSZ formed. Subsequent heating in air led to particle growth. However, even when the particles were heated to a temperature as high as 10003C, the particle size was well in the nanosize range.