Well-dispersed tin(IV) oxide (SnO2) nanosize crystallites were prepared by a novel liquid-phase process using Na2SnO3 precursor of several micrometers in size. The product was characterized using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and BET. The nanosize SnO2 powder formed has a narrow particle size distribution ranging between 1 and 7 nm, a very high surface area, and crystallizes in the tetragonal structure. A possible mechanism for the liquid-phase process, which is a combined effect of coprecipitation, hydrolization, and molecular decomposition, is proposed.