To increase the performance of solid oxide fuel cell operating at intermediate temperature (600oC~800oC), Sm0.2Ce0.8O2 (SDC) thin layer was applied to the La0.8Sr0.2Mn0.8Cu0.2O3 (LSMCu) cathode by sol-gel coating method. The SDC was employed as a diffusion barrier layer on the yttria-stabilized zirconia(YSZ) to prevent the interlayer by-product formation of SrZrO3 or La2Zr2O7. The by-products were hardly formed at the electrolyte-cathode interlayer resulting to reduce the cathode polarization resistance. Moreover, SDC thin film was coated on the cathode pore wall surface to extend the triple phase boundary (TPB) area.