Fuel cells are considered to be a promise device to convert chemical to electrical energy that exhibits main advantages such as high efficiency and low environmental impact. Among different kinds of fuel cells, solid oxide fuel cells (SOFCs) have received tremendous attention due to their high efficiency, low pollution, and high flexibility of fuels, in high operation temperature. The traditional SOFCs that operated at high temperature, 800-1000 ?C, has some problems related to the cost of the materials and fabrication. However, high operation temperature is useful in increasing the rate of electrode reactions and decreasing the cell ohmic resistance. possibility of additional reaction between cell components, increase the need to use costly metal interconnects. Therefore, an important research is to get lower cost components for operation temperatures under 800 ?C. Accordingly, intermediate temperature solid oxide fuel cells (IT-SOFC), operating in range 600-800 ?C temperatures, have attracted much attention in recent years. Reduction of SOFC operating temperature under the 800 ?C range allows for a greater choice of materials. To counteract the increased ohmic resistance across the electrolyte during reduced temperature operation and improve cell performance, micro-SOFCs (µ SOFCs) utilizing thin film component are being actively developed. One of the vital SOFC components is the cathode with important characteristic of high electrical conductivity and sufficient ionic conductivity. In particular, perovskite materials are well known for their more than adequate characteristics as SOFC cathode materials. Studies on the mixed electronic and ionic conduction (MIEC) materials show that Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 (BSCF) is a good candidate to be used in intermediate solid oxide fuel cells. In this study, powder of BSCF oxide was prepared by two solid state reaction and sol-gel methods for solid oxide fuel cell cathode applications. Furthermore, to investigation of oxygen pressure impact, thin films of BSCF have been grown successfully on single crystal SrTiO 3 (STO) and Si substrates in different oxygen pressures by pulsed laser deposition (PLD). Crystal structures of bulk and thin films were studied by X-Ray Diffraction (XRD). X-Ray patterns of Bulk show monoclinic cubic structure. The XRD pattern obtained for thin films on STO substrate showed a preferred (00 l ) crystalline orientation in the direction of substrate. The surface morphology of films was analyzed by atomic force microscope (AFM). The films surface consist of different separated BSCF islands. The diameter and height of this islands increase with oxygen pressure in such a way so that spherical island are formed in higher oxygen pressure. The electrical resistivity of bulk and thin films were measured from room temperature up to operation temperature of IT-SOFC (800 ?C) by four-point probe method in air atmosphere, that showed a sharp drop compared to initial value for bulks and thin films. Furthermore, it has shown that increasing of oxygen pressure obtain thin films with lower initial resistance. The surface exchange coefficient (K chem ) of the BSCF thin film, determined by electrical conductivity relaxation (ECR) technique. The conductivity change was sharp upon the sudden switch in oxygen pressure and followed an exponential relaxation curve, which well fit with electrical conductivity relaxation model. Results show that BSCF is a good candidate to be used as cathode in intermediate solid oxide fuel cells and µSOFCs structure. Keywords: Solid Oxide Fuel Cell, Cathode, Perovskite, Pulsed Laser Deposition, Thin Film, Electrical Resistance.