Homogeneous yttria-stabilized zirconia (YSZ) with 8–31 nm average crystallite andparticle diameter containing 3–10 mol% yttria are made by flame spray pyrolysis(FSP) of various yttrium and zirconium precursors at production rates up to350 g h−1. Product particlesare characterized by N2 adsorption (BET), transmission electron microscopy (TEM), energy-dispersive x-rayspectroscopy (EDS) and x-ray diffraction (XRD). The effect of liquid precursorcomposition on product particle morphology, composition and crystallinity isinvestigated. The yttria content does not affect the product primary particle andcrystal sizes of homogeneous YSZ. These are determined, in turn, by the processenthalpy content and overall metal concentration. Flame-made YSZ nanoparticles ofhomogeneous composition and morphology are formed when using either onlyorganometallic zirconium and yttrium precursors or 2-ethylhexanoic acid as solvent andinexpensive zirconium carbonate and yttrium nitrate hexahydrate as precursors.In contrast, and consistent with the literature, hollow or inhomogeneous YSZparticles are made when organometallic zirconium and yttrium nitrate precursors ofhigh water content are employed, especially at high production rate. The ratioof XRD-determined small to large sizes for inhomogeneous crystalline particlesis an effective quantitative measure of their degree of inhomogeneity. For suchinhomogeneous particles nitrogen adsorption is not a reliable technique for theaverage grain size as it relies on integral properties of the particle size distribution.