Sm0.5-xBaxSr0.5Co0.8Fe0.2O3-δ powders were synthesized by a sol-gel method. The crystal structure and thermal expansion coefficient of Sm0.5-xBaxSr0.5Co0.8Fe0.2O3-δ (SBSCF, x=0.00, 0.05, 0.10) were investigated. All samples were the perovskite structure with an orthorhombic symmetry and exhibited a similar thermal expansion behavior. The electrochemical properties of SBSCF-SDC composite cathodes were studied using A.C. impedance method. The substitution of Ba2+ for Sm3+ had a significant effect on the area specific resistance of the composite cathodes. The area specific resistance (ASR) decreased with the increase of Ba2+ substitution. This result suggested that the electrochemical performance of Sm0.5Sr0.5Co0.8Fe0.2O3-δ based cathode improved as Sm3+ is partially substituted by Ba2+.