Abstract: An ionic conductor has been developed which exhibits both hydrogen ion conductivity and electronic conductivity. The conductor is a perovskite-type oxide represented by the general formula: ABO3 where A consists of at least one element selected from the group consisting of Ba, Ca, Mg and Sr and B is Ce1-xMx where M is a multivalent dopant metal, preferably Eu or Tb, and x is greater than 0 and less than 1. It is particularly useful in processes in which hydrogen is separated from a hydrogen-containing gas, e.g. in conversion of natural gas, operation of hydrogen fuel cells, etc.