This paper presents a hydrothermal method for synthesizing tin-doped indium oxide (ITO) powder. It shows that monodispersed ITO powders of diameter 70 +/- 10 nm can be readily prepared by a process using NaOH as a basic source and involving hydrothermal synthesis at 240 degrees C in 12 h and post-calcination at 500 degrees C. The powder size is decreased by increasing the initial indium and tin concentration ([In+ Su](precursor)) and the excess NaOH concentration ([NaOH](excess)) in the solution. The proposed technique has a significant potential for the commercial production of ITO nanopowders.