Indium tin oxide (ITO) particles of 20-30 nm in diameter, which would be used as coating material for electromagnetic wave shield, were synthesized by co-precipitation of indium chloride and tin chloride. Size and shape of particles were controlled by pH of co-precipitation solution, thermal oxidation temperature and tin contents. The prepared particles were thermally reduced under hydrogen gas to control electrical properties. When the solution pH was 6.75, plate type of particles with 60 nm size was coexisted with spherical particles of 20 nm size and the part of crystal structure was hexagonal. As pH was increased, plate type of particles was disappeared and 20-30 nm size of spherical particles were formed. Size of ITO particles was increased and particle resistance was decreased with increasing thermal oxidation temperature of indium tin hydroxide in the range of 400-700 degreesC. Particle size was decreased as tin content was increased from 3.18 to 21.11 at.% Sn/In in co-precipitation. The resistance of particles had a minimum point with changing of tin contents. The lowest resistance was shown in the region of about 3-5 at.% Sn in ITO. It was confirmed by Auger electron spectroscopy (AES) that tin ratio of ITO particle was increased with increasing tin contents. (C) 2004 Elsevier B.V. All rights reserved.