Yttria-stabilized zirconia (YSZ) nanoparticles were synthesized in supercritical water (SON) without the use of mineralizers that are conventionally used to ensure basic conditions during synthesis. Process parameters were varied and their effect on the synthesis yield and particle morphology and composition were investigated. Conditions for synthesizing a stoichiometric YSZ nanopowder were identified. Dry YSZ particles collected in the continuous SCW process were redispersed in water in order to study their aggregation characteristics (including the size of agglomerates and the degree of agglomeration) in aqueous dispersions. Surface modification by the addition of polyethylenimine (PEI) was shown to result in stable dispersions of particles with average diameters between 50 nm and 100 nm. (C) 2012 Elsevier B.V. All rights reserved.