Samaria doped ceria (Ce0.8Sm0.2O1.9, SDC) was prepared by the improved Pechini method. The phase of the SDC was studied by XRD, which showed that it formed single phase after being sintered at 500 oC. The TEM showed that the size of particle was about 10 nm. The conductivity of the SDC pellet was higher than the sample prepared by the oxalate coprecipitation process and glycine–nitrate process. A series of ceria-based composite materials consisting of samaria doped ceria (SDC) and binary carbonates (Li2CO3–Na2CO3) were examined as functional electrolytes. Their structure, morphology and ionic conductivity were investigated. A transition of ionic conductivity with temperature was occurred among all samples with different carbonate content, which related to the interface phase. The interfacial polarization resistances of the cathodes were determined from the impedance spectra of symmetric cells. The polarization resistance for lithiated NiO cathode was as low as 0.05 Ωcm2 at 600 oC. The single cells were fabricated by a simple dry-pressing process and tested at 400-600 oC. A maximum power density of 1Wcm-2 and the open-circuit potential (OCP) of 1 V was achieved at 600 oC for a single cell based on composite electrolytes, NiO as anode and lithiated NiO as cathode, with carbonate content of 25 wt.%. During fuel cell operation, it found that the SDC-carbonate composites are co-ionic (O2-/H+) conductors. The stability of the cell has been examined for more than 100 h at different temperatures, which showed that the cell operated stably at 500–600 oC with excellent performances.