BaCeO 3 based ceramics have demonstrated high proton conductivity and have been extensively investigated as electrolytes for solid oxide fuel cells (SOFCs). However, these materials are not chemically stable and are prone to reaction with CO 2 in air at the typical SOFC operating conditions. This work presents a novel strategy to improve the chemical stability of BaCeO 3 based ceramics to CO 2 in air while still maintaining high proton conductivity by introducing barium chloride precursor in the powder synthesis process. As an example, BaCe 0.8 Sm 0.2 O 3−δ with Cl doping has demonstrated significant enhancement in chemical stability in the presence of CO 2 in air without compromising its high proton conductivity.