Abstract: In a supported catalyst for treating internal combustion engine exhaust gases the active material comprises a non-noble metal or compound thereof and the support comprises a primary support carrying a secondary support; the secondary support consists essentially of one or more involatile acidic and/or amphoteric oxides substantially in combination with one or more basic oxides from Group II, III or IV of the Periodic Table. A platinum group metal may also be present. The catalyst can be used for reductive or oxidative treatment or for simultaneous reduction of nitrogen oxides and oxidation of carbon monoxide and hydrocarbons and exhibits high activity and long life.