Abstract: An indium oxide-tin oxide powder for ITO display devices etc. with only slight variance in properties such as average particle diameter and apparent density is prepared stably with good controllability and at low cost: (1) by electrolyzing indium as an anode, calcining or roasting the indium hydroxide obtained and combining the resulting indium oxide powder with a tin oxide powder; (2) by electrolyzing tin as an anode, calcining or roasting the metastannic acid obtained and combining the resulting tin oxide powder with an indium oxide powder; (3) by simultaneously electrolyzing indium and tin as separate anodes and then calcining or roasting the resulting mixed precipitate of indium hydroxide and metastannic acid to produce an indium oxide-tin oxide powder; or (4) by electrolyzing an alloy of indium and tin as an anode and then calcining or roasting the resulting precipitate of indium hydroxide and metastannic acid to produce an indium oxide-tin oxide powder.