We report on the synthesis of In2O3 nanostructures grown at three different growth temperatures by using the thermal evaporation method. The obtained nanostructural morphologies of In2O3 were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In2O3 nanopencils and pyramidal monument-like structures were reported. The reaction temperature and the difference of temperature between the central heating zones and the product deposition zones, the reaction time, and the surface energies of different growth planes are all responsible for the final crystalline morphologies of the In2O3 nanostructures. A growth mechanism proposed to elucidate the kinetic factors leading the growth of In2O3 nanostructures. The obtained results may not only assist the investigation of new approaches of preparing various nanostructures for potential technical applications and how to modulate the desired morphology, but also give a deeper understanding of the fundamental physical and chemical processes of CVD methods.