Nanoscaled so called indium tin oxide In2O3:Sn (ITO) with a specific BET surface area of 50 m2/g to 60 m2/g was prepared via an electrochemical method in an aqueous system containing ammonium acetate as conductive salt. As an intermediate product of the synthesis nanocrystalline In(OH)3is obtained which serves as a precursor for the subsequent calcinations accompanied by tin doping resulting in ITO powders with various tin concentrations. Its phase transitions and the reduction behaviour of hydroxide to oxide during the calcination process in air flow and forming gas atmosphere of N2to H2ratio of 95 to 5 respectively, have been investigated by high temperature X-ray diffraction, TG/DSC/MS, HRTEM and SEM analysis. Depending on the atmosphere dehydration of tin doped In(OH)3started at 150 °C, cubic ITO solid solution formed between 190 °C and 300 °C. The total weight loss of the hydroxide of approx. 21% occurred mainly below 360 °C and the burn-out of organic components mainly between 308 °C and 316 °C. The results of DSC and MS analyses were in good agreement with the results of the X-ray diffraction. In addition, the products have been characterized by EDX associated with TEM, XPS, ICP-AES, BET analysis and119Sn Mössbauer spectroscopy. Completely reacted samples of ITO have been processed to pellets, calcined and sintered in the temperature range between 900 °C and 1100 °C and characterized by measurements of the electrical conductivities of bulk and surface in the reduced as well as in the oxidized state giving values up to 1400 Scm−1.