In this study, BaCeErO was synthesized by a microemulsion method. Then, a BaCeErO-KSO-BaSO composite electrolyte was obtained by compounding it with a KSO-LiSO solid solution. BaCeErO and BaCeErO-KSO-BaSO were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry. AC impedance spectroscopy was measured in a nitrogen atmosphere at 400-700 °C. The logσ~log () curves and fuel cell performances of BaCeErO and BaCeErO-KSO-BaSO were tested at 700 °C. The maximum output power density of BaCeErO-KSO-BaSO was 115.9 mW·cm at 700 °C, which is ten times higher than that of BaCeErO.