Ceria is proposed as an additive for La0.8Sr0.2MnO3 (LSM) cathodes in order to increase both their thermal stability and electrochemical properties after co-sintering with an yttria-stabilized zirconia (YSZ) electrolyte at 1350 °C. Results show that LSM without CeO2 addition is unstable at 1350 °C, whereas the thermal stability of LSM is drastically improved after addition of CeO2. In addition, results show a correlation between CeO2 addition and the maximum power density obtained in 300 μm thick electrolyte-supported single cells in which the anode and modified cathode have been co-sintered at 1350 °C. Single cells with cathodes not containing CeO2 produce only 7 mW cm-2 at 800 °C, whereas the power density increases to 117 mW cm-2 for a CeO2 addition of 12 mol%. Preliminary results suggest that CeO2 could increase the power density by at least two mechanisms: (1) incorporation of cerium into the LSM crystal structure, and (2) by modification or reduction of La2Zr2O7 formation at high temperature. This approach permits the highest LSM-YSZ co-sintering temperature so far reported, providing power densities of hundreds of mW cm-2 without the need for a buffer layer between the LSM cathode and YSZ electrolyte. Therefore, this method simplifies the co-sintering of SOFC cells at high temperature and improves their electrochemical performance.