We prepared crystalline SnO2 particles from aqueous solutions of SnCl4 with and without citric acid via hydrothermal treatment. The crystallinity, the crystallite size and shape, and the morphology of the secondary particles depend on the concentration of citric acid, the pH value of the solvents and the hydrothermal treatment temperature. Spherical SnO2 particles of 1-3 mu m in diameter consisting of nanocrystallites below 10 nm in size were obtained via hydrothermal treatment at 150 degrees C from a solution with the citric acid/SnCl4 mole ratio of 0.5 in acidic solvents of pH 3.0-5.5. The SnO2 spheres were thought to be formed through the moderate nucleation rate provided by the relatively high solubility of Sn4+ species and coordination by citric acid. (C) 2011 Elsevier B.V. All rights reserved.