A plasma synthesis method has been devised to produce nanosize YSZ powders with various yttria contents. The powders are synthesized by introducing a mixture of coarse-grained zirconia and yttria into an r. f. inductively coupled plasma flame. The average particle size of the as-prepared powders is in the range 20 40 nm and the specific surface area is 18 50 m(2) g(-1). The phase and granulometric composition of the produced powders depend on the degree of evaporation of raw powders, reagent concentration in the gas flow and quenching rate, and on the content of Y2O3. Up to 5.5 mol% yttria, the major phase of nanosize powders is tetragonal ZrO2, mostly as the non-transformable (t＇) form. For yttria contents higher than 6 mol%, the major phase is cubic ZrO2.