The structure and nature of perovskite-type complex oxides ( PTO) is discussed in detail in this paper. PTO can make different functional material based on the formation of PTO with oxygen vacancies by the substitution of A-site and B-site cations with other appropriate cations. PTO are used widely in SOFC because of their high conductivity and good catalytic activity as well as high chemical stability and thermo - stability in high temperature. The typical PTO such as LSM,LSCF, used as cathode for SOFC have been discussed in detail in the paper.