Nanocrystalline SnO 2 with different particle sizes has been prepared by means of hydrothermal precipitation. The resulting SnO 2 nanometer size powders, which are basically spherical in shape according to TEM, are tetragonal in structure with space group P4/mnm. Calculation shows that the crystallite size of SnO 2 increases with increase of the calcination temperature, but that the average crystal lattice distortion rate decreases with increase of crystallite size. The smaller the particle, the bigger the crystal lattice distortion and the slower the crystal growth rate. Weight loss analysis indicates the prepared SnO_2 is very slightly impure.