Large scale, uniform Er2O3 microspheres have been prepared with CO(NH2)(2) as the precipitant through a hydrothermal method. The obtained products were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field-emission scanning electron microscopy. The Er2O3 microspheres are composed of nanoparticles, and the diameter is in the range of 200-300nm. In addition, a possible formation mechanism of Er2O3 microspheres was discussed.