Indium oxide, a wide band gap transparent conductor, is of great interest for many device applications due to its unusual combination of high transparency in the visible region and high electrical conductivity. Several methods, comprising all three phases, namely, the solid phase, the solution phase, as well as the vapor phase, have been used for the preparation of In2O3 powders and thin films. In this work, indium oxide nanoparticles were synthesized by homogeneous precipitation using hexamethylenetetramine as ligand and indium nitrate or indium chloride as precursor materials. Thermogravimetry and differential thermal analysis results evidenced the relatively low temperature for crystallization of indium oxide. Spherical clusters consisting of about 8 nm of diameter indium oxide nanoparticles were obtained after thermal decomposition at 400 °C for 2 h, as revealed by X-ray diffraction experiments and nitrogen adsorption measurements. Transmission electron microscopy observations confirm the single-crystalline nature of the prepared nanoparticles. This material exhibits photoluminescence emission at room temperature with peak onset at 315 nm as a consequence of the small size of the particles.