Since crystals of Sn0_2 Were prepared by vapour-phase reaction method from anhydrous SnI_4 powder. The single crystals were characterized by optical microscope and X-ray Lang camera in order to clear the growth mechanism and internal defects in them. A Iot of black dots were observed in the Lang topograph. It seems that the dots are planar defects with the Magneli structure in the crystal. The single crystals were grown by the Kossel mechanism.