Formation of spherical, micron-sized ceramic particles was investigated in an RF thermal plasma reactor. It has been concluded that a wide size distribution of feedstock powders gives rise to either excessive evaporation of smaller grains or insufficient melting of bigger ones. Ceramic spheres with more or less voids inside can also be prepared starting from powders pretreated in special ways. (C) 2004 Elsevier B.V. All rights reserved.