Properties and applications as a pH sensor of Y2O3-doped CeO2 films prepared by r.f. magnetron sputtering were studied. The CeO2-Y2O3 films exhibited higher electric conductivity than yttria-stabilized zirconia. Films deposited on an MgO single-crystal (100) substrate without substrate heating had a more dense structure. The microstructure of the samples deposited at a substrate temperature of 873 K was shown to be columnar by scanning electron microscope. X-ray diffraction studies showed that a (111) diffraction peak assigned to CeO2 was much greater and the films exhibited preferential orientation to the (111) plane with increasing r.f. power or substrate temperature. The pH electrode was made by a double layer of Y2O3-doped CeO2 and Cu/Cu2O redox films deposited onto the MgO substrate, pH response was measured in various pH buffer solutions at room temperature. It showed good agreement with a nernstian response in the pH range 9-13.