Single-crystal tin oxide (SnO2) nanostructures with rutile structure have been synthesized through a facile hydrothermal process. The morphologies and structural properties of the nanorods/nanoneedles/nanowires were characterized by scanning electron microscopy (SEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). The SEM images reveal tetragonal nanoneedles in cross-sectional view. The XRD peaks indicate a typical rutile phase of the SnO2. The effects of the synthesis parameters on the growth mechanism are discussed.