YBa2Cu3Ox, known as a high-Tc superconductor, was used as an electroconductive catalyst and its characteristics in CO oxidation were investigated. Charging 3 V, direct current, heated YBa2Cu3Ox up to about 500 degrees C, at which it could catalyze CO oxidation. Thus, this oxide has proper features required for electrically temperature-controlled combustion catalysts : one is self-heating property caused by electric current (Joule’s heat) and the other is catalytic activity for combustion. The catalytic activity of YBa2Cu3Ox was greatly affected by the oxygen deficiency in the solid which was directly related to the partial pressure of oxygen in the reaction system.