beta-In2S3 powders with particles having an average size of 13 nm and spherical shape have been successfully prepared through the hydrothermal treatment of a sol from indium trichloride and sodium sulfide at 140 degrees C. The effects of temperature, time, and the pH value of the sol on the formation of the nanocrystalline beta-In2S3, powders were investigated. The products were char acterized by powder X-ray diffraction (XRD), transmission electron micrography(TEM), and IR spectroscopy.