Preparation of indium-tin oxide(ITO) powder by oxalic acid from metallic indium and tin was investigated. The intermediate(indium-tin oxalate salt) was formerly prepared at various conditions, and thermal decomposition was followed to obtain ITO powder for ITO target. Optimum conditions for preparation of the intermediate were oxalic acid concentration 2.0M, pH 8.0, reaction temperature 80 ℃ and reaction time 6 hours. The purity of the intermediate could be increased by recrystallization up to 99.99% (4 N). The phase transition temperature of the intermediate to ITO powder was analyzed by TGA. The purity, crystal structure and particle shape of ITO powder were examined by ICP-OES, XRD and TEM, respectively. ITO powder obtained was spherical, whose size was 20-50 nm.