ZrO2: 3mol% Y2O3 powders were mixed in different proportions to ZrO2: 8 mol% MgO, pressed and sintered at 1500°C for producing composites with oxygen ion conductivity better than that of ZrO2: 8 mol% MgO and thermal shock resistance better than that of ZrO2: 3 mol% Y2O3. The electrical conductivity was evaluated by the impedance spectroscopy technique at 600°C as a function of the partial pressure of oxygen using zirconia-based oxygen pump and sensor. The thermal shock resistance was studied by room temperature- 1550°C dilatometry on sintered pellets. Moreover the composites were studied by X-ray diffraction and scanning electron microscopy. All composites are partially stabilized in the monoclinic-tetragonal phase and the apparent density is higher than 90% of the theoretical density. The thermal shock behavior of the composites is similar to that of ZrO2:8 mol% MgO materials used in disposable high temperature oxygen sensors. The electrical response of the composites at high temperatures is better than the electrical response of ZrO2:8 mol% MgO.