An unusual nanorod growth phenomenon is described. Indium sesquioxide (In 2O 3) nanorods with diameter of 20 nm and length up to several hundreds nanometers were formed on the surface of commercial anodic aluminum oxide (AAO) membranes through calcination of InCl 3·4H 2O at 500 °C. The growth of In 2O 3 in the form of short rods, instead of the particulates commonly encountered in calcination processes, was believed to be induced by the thin frame of the net-shape structure on the AAO membrane surface. The particulate form of In 2O 3 was obtained in the absence of the net-shape structure or in the presence of non-net-shape structure. Photoluminescence (PL) measurement at room temperature showed two emission peaks at 405 and 462 nm, with the former attributable to the near band edge emission of In 2O 3 and the latter resulting from the common oxygen deficiency in In 2O 3. X-ray diffraction and electron diffraction patterns indicated that the In 2O 3 nanorods were in a polycrystalline cubic phase. The unusual growth mechanism of In 2O 3 nanorods offers a simple and convenient alternative synthetic route for one-dimensional structures of In 2O 3 and possibly other materials.