BaCe0.8-xNbxSm0.2O3-d (x = 0, 0.05, 0.1) powders were prepared by a solid-state reaction method. After boiling in water for 3 h, the BaCe0.8Sm0.2O3-d powders obviously decomposed into CeO2 and BaCO3 while the other two powder samples containing Nb element in B site were hardly affected. According to thermal gravity analysis, the BaCe0.8Sm0.2O3-d powders displayed obvious reaction with CO2 while the BaCe0.7Nb0.1Sm0.2O3-d powders were quite stable. Moreover, the sintered BaCe0.7Nb0.1Sm0.2O3-d sample exhibited a conductivity value of 0.0026 S/cm at 700 C in wet hydrogen. A fuel cell with BaCe0.7Nb0.1Sm0.2O3-d as electrolyte was prepared by a suspension spray combining with in situ sintering method and tested in hydrogen from 600 C to 700 C. The peak power densities respectively reached 245 mW/cm2 at 700 C, 110 mW/cm2 at 650 C and 75 mW/cm2 at 600 C. The interface resistances were 0.31 O cm2 at 700 C, 0.43 O cm2 at 650 C and 1.2 O cm2 at 600 C, correspondingly.