The structure and performance of Sm0.5Sr0.5Co0.4M0.6O3(M=Co, Mn, Fe|denoted SSCC, SSCM and SSCF, respectively) as intermediate temperature-solid oxide fuel cells (IT-SOFCs) cathodes were investigated by X-ray diffraction (XRD), thermogravimetry (TG), thermal expansion, electrical conductivity and electrochemical impedance spectroscopy (EIS). The Sm0.5Sr0.5Co0.4M0.6O3 system has an orthorhombic structure. The crystal parameter increases in the following order: Co, Mn, Fe, while the oxygen content, thermal expansion and electrical conductivity decrease in the same order. The electrocatalytic activity of SSCMcathodes is limited by the oxide ion diffusion process because of low oxide ion vacancy, while the electrocatalytic activity of SSCC or SSCF is controlled by an oxygen exchange process on the cathode surface and an oxide ion diffusion process in the cathode because of the high oxide ion vacancy. The area specific resistance (ASR) of SSCF is lower than that of the SSCC above 700 ℃ because of the high oxide diffusion coefficient of SSCF, so the total electrocatalytic activity of SSCF is higher than that of SSCC.