The　BaCe0.8Y0.2O2.9-Ce0.8Gd0.2O1.9　(BCY-GDC)　composite　electrolytes　with　different　molar　ratios　were　prepared　a　mechanically-mixing　method　using　BCY　and　GDC　powders　prepared　via　a　sol-gel　combustion　method,　and　were　sintered　in　air　at　1450℃　for　5　h.　The　chemical　stability　and　electrochemical　properties　of　BCY-GDC　composite　electrolytes　were　investigated.　The　results　show　that　the　chemical　stability　of　BCY-GDC　composite　electrolyte　against　CO2　and　boiling　water　is　better　than　that　of　the　single　phase　BCY.　The　BCY-GDC　composite　electrolytes　have　a　good　chemical　stability　against　CO2　and　boiling　water　as　the　molar　ratio　of　BCY　is　less　than　70%.　The　single　cell　made　from　the　BCY-GDC　composite　electrolyte　with　a　BCY-GDC　molar　ratio　1:1　possesses　better　stability　of　the　maximum　power　density　than　the　cells　with　the　BCY　electrolyte　at　700℃　for　20　h.　©　2016,　Editorial　Department　of　Journal　of　the　Chinese　Ceramic　Society.　All　right　reserved.