The catalytic activity of indium-supported TiO2-ZrO2 binary metal oxide for the selective reduction of NO with propene in the presence of oxygen was investigated. The supported indium caused a drastic enhancement of NO reduction activity of TiO2-ZrO2. It was suggested that the "dispersed phase" of indium oxide, which is reduced at lower temperature in temperature-programmed reduction (TPR), is responsible for the high activity. Propene served as the most efficient reducing agent, while oxygenated hydrocarbons were not good ones. A reaction mechanism was proposed that N-2 is formed through the reaction of propene and NO2, which was formed on the acid sites of TiO2-ZrO2, on the indium sites.