Oxidation characteristics of Si 0.85 Ge 0.15 nanowires were investigated using transmission electron microscopy (TEM) analyses. Si 0.85 Ge 0.15 nanowires were grown in a tube furnace by vapor–liquid–solid (VLS) method and thermally oxidized at 925°C for 1–8h. After oxidation, oxide thicknesses were measured using TEM images. Si 0.85 Ge 0.15 nanowires showed a thicker oxide than Si nanowires, for the whole range of oxidation time. The oxidation rate of Si 0.85 Ge 0.15 nanowires significantly decreased in nanowires with diameters less than 150nm. Long-term oxidation in Si 0.85 Ge 0.15 nanowire resulted in the oxidation of germanium atoms.