To make titanium tin oxide (TTO) adapted to serve as a catalyst as well as a ground electrode in a DC corona discharge gas purifier, indium tin oxide (ITO) with low resistivity was composited with TTO via the sol gel method. The resistivity of TTO ITO composite was reduced to ca. 5 from ca. 10(4) Omega cm of TTO. The discharge characteristics and the purification performance were promoted by the reduction of resistivity. There was no difference between TTO ITO and TTO in valence states or crystal phases. We deduced that the hybrid purification mechanism of purifier TTO ITO was plasma catalysis driven by electrons.