Silicon nanowires have received attention for nanoscale electronic devices and chemical and biological sensors. The thermal oxide grown on the silicon nanowires could be used in a variety of devices, so the oxidation of the silicon nanowires is investigated in this work. Silicon nanowires with an average radius of 37nm were grown for these experiments using the vapor-liquid-solid technique with Au to mediate the growth. Etching of the Au tips from the silicon nanowires was performed prior to oxidation to avoid local accelerated oxidation at the nanowire tip. Oxidation was performed at 700°C for 1–121h and at 650 and 750°C for 4h in O2, and the oxidized nanowires were examined by transmission electron microscopy. Depending on the conditions for oxidation, an oxide shell as thin as 6nm was observed, or the entire nanowire was oxidized. The kinetics of oxidation differ from those of a planar silicon wafer and are discussed in this work.