In this study, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 (BSCF) oxide was prepared, using a solid state reaction method. This composition was investigated as a cathode of fuel cell. Crystal structure and electrochemical conductivity were studied by x-ray diffraction and four -point DC, respectivly. The x-ray pattern shows cubic structure. The resistivity was measured from room temperature up to 400?C. At this temperature range, resistivity was dropped 99 percent of its original value. In the investigation of the electrochemical properties, D chem , chemical diffusion coefficient and E a , activation energy for hopping of small polarons were calculated. Hopping of small polaro can attribute to conductivity mechanism. The results demonstrated that by increasing temperature the value of D chem is enhanced. Relation between LogD chem and temperature inverse i linear with negative slope.