Using x-ray Rietveld analysis the fcc (fluorite-type) structure of a Na-containing nanocrystalline zirconia powder (9.5 nm estimated crystallite size) obtained by precipitation and calcination has been confirmed. The result shows that conventional x-ray diffraction techniques can distinguish the cubic crystallographic form of ZrO2 from the tetragonal one in nanosized powders. These conclusions are supported by independent Raman scattering experiments.