Indium oxide manufacturing process from waste indium tin oxide (ITO) targets by oxalic acid was experimentally studied. The process was composed of precipitation of intermediate (indium-oxalate salt), re-crystallization and its thermal decomposition. The waste ITO targets were generated from vacuum sputtering process. The effects of operating parameters, such as solid dosage, oxalic acid concentration, reaction temperature and time, on the precipitation and re-crystallization of indium-oxalate salt were examined. Thermal decomposition to indium oxide was also investigated. The optimum reaction conditions to indium-oxalate salt were oxalic acid concentration 1.5M, solid dosage 50 g/L, reaction temperature 80 °C and reaction time 8 hours. The purity of indium-oxalate salt prepared by precipitation and re-crystallization was 99.99% (4 N), and the salts were thermally decomposed to indium oxide at over 600 °C. The purity of the final product, indium oxide, was dependent on that of the intermediate, indium oxalate salt.