Monodisperse non-aggregated spheroidal nanoparticles of SnO 2 cassiterite are prepared through hydrolysis of tin isopropoxide in the presence of acetylacetone and p-toluenesulfonic acid, followed by ageing at 60 uC. The obtained sols remain stable for several months at 4 uC. The nanoparticles have been characterized in the solid state (xerosol) by powder X-ray diffraction, TEM, FTIR, TGA-DTA, and 119 Sn MAS and 13 C CP-MAS NMR. The mean size of the cassiterite oxide core is about 1-2 nm. These particles do not aggregate in suspension because their surfaces are protected by an hybrid organic-inorganic layer containing acetylacetonate ligands, acetylacetone, p-toluenesulfonates and water.