Hollow silica spheres (HSSs) are prepared via a two-step method: producing micrometer-sized agglomerated granules with nano-silica by spray drying and spheroidizing and hollowing the spray-dried granules (SDG) by DC thermal plasma sintering. The morphology, particle size distribution and porosity of SDG are affected by the solid concentration of the slurry. The shell structure and shell thickness of HSSs can be tuned by plasma sintering different kinds of SDG. The cavity formation mechanisms of two different types of HSSs, including single large void and multiple small voids are further investigated. The DC thermal plasma sintering method provides a facile way to produce HSSs with low density and high crush strength which have promising applications in many fields. (C) 2014 Elsevier B.V. All rights reserved.