Morphology-and size-controlled In（OH）3 nanocrystals were synthesized via a novel, low-cost and low-temperature （70°C） route in the absence of any template and surfactant. The as-prepared products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and high-resolution transmission electron microscopy （HRTEM） with selected area electron diffraction （SAED）. The morphology and size of In（OH）3 nanostructures can be controlled by adjusting the reaction conditions such as the reaction time, the concen-tration of the alkali, and the alkaline source. A possible mechanism for the evolution of the morphology- and size-controlled In（OH）3 was proposed. In addition, the optical properties of the In（OH）3 prepared by this method were studied by diffuse reflection spectra （DRS） and photoluminescence （PL） spectroscopy, and the results exhibit an obvious change of adsorption edges. The thermal behaviors of the as-prepared products were also explored by thermo-gravimetric （TG） and differential scanning calorimetry （DSC） measurements. According to the results of TG-DSC, the pure phase and uniformity of the In2O3 nanocube and nanorod can be obtained by annealing In（OH）3 precur-sors directly at 300°C.
