BaCe0.8Y0.2O2.9-Ce0.8Gd0.2O1.9(BCY-GDC,　molar　ratio　1:1)　composite　electrolytes　were　prepared　via　sol-gel　combustion　method　and　mechanically-mixing　method.　The　BCY-GDC　pellets　were　sintered　in　air　at　1550℃　for　5　h.　The　chemical　stability　and　electrochemical　properties　of　BCY-GDC　composite　electrolyte　were　investigated.　The　results　show　that　BCY-GDC　composite　electrolyte　sintered　at　1550℃　promote　the　solid-state　reaction　between　BCY　and　GDC,　then　produce　a　perovskite　phase　of　BaCe1-x-yGdxYyO3-α.　The　chemical　stability　against　3%CO2　at　the　temperature　of　700℃　and　boiling　water　of　the　BCY-GDC　pellet　after　solid-state　reaction　is　higher　than　that　of　the　single　phase　BCY.　The　single　cell　with　BCY-GDC　composite　electrolyte　after　solid-state　reaction　also　shows　a　better　stability　of　the　open　circuit　voltage　and　max　power　density　than　that　of　the　cells　with　the　BCY　electrolyte　at　700℃　for　20　h.　©　2016,　Chinese　Ceramic　Society.　All　right　reserved.