Porous and polycrystalline In2O3 nanotubes are prepared by layer-by-layer assembly on CNT templates and subsequent calcination (see figure). The as-prepared In2O3 nanotubes exhibit superior sensitivity to NH3 at room temperature, as well as a good reproducibility and short re sponse/recovery time. This novel approach presented herein can be extended to synthesize other metal oxide nanotubes such as NiO, SnO2, Fe2O3, and CuO.