By using X-ray diffraction lattice parameter measurements and Raman spectroscopy studies, the solid solubility limits of titania in ceria tetragonal zirconia solid solutions (12 mol% CeO 2 ) have been established. Electrical properties of the mixed conductor TiO 2 -Ce-TZP containing 5 and 10 mol% TiO 2 were measured at the 300 o C-900 o C temperature range. The total electrical conductivity in air of the TiO 2 -Ce-TZP ceramics decreases with titania content due to Ti-Vo associations, which depresses the mobility of the oxygen vacancies during the conduction process. The electrical behaviour of undoped-Ce-TZP solid solutions as a function of the pO 2 and temperature showed that in oxidising conditions and up to an oxygen partial pressure of 10 - 9 Pa the materials were nearly pO 2 independent. Under lower oxygen partial pressure the total electrical conductivity increases according to pO 2 - 1 / 6 indicating that the n-type conduction in Ce-TZP is due to the electron hopping between Ce 4 + and Ce 3 + cations. In Ce-TZP containing 5 and 10 mol% titania the electrical behaviour was very different mainly under the most reducing conditions. Above 800 o C and with decreasing oxygen partial pressure below 10 - 9 Pa, the theoretical correlation for electronic conduction was near to n pO 2 - 1 / 4 , which indicates that the conduction process is controlled by the Ce' Z r and Ti' Z r defect concentrations, by hopping of the electrons between Ce 4 + and Ce 3 + and Ti 4 + and Ti 3 + via a small polaron hopping mechanism.