A cathode layer and a membrane electrode assembly of a solid oxide fuel cell are provided. The cathode layer consists of a plurality of perovskite crystal films, and the average change rate of linear thermal expansion coefficients of these perovskite crystal films is about 5% to 40% along the thickness direction. The membrane electrode assembly includes the above-mentioned cathode layer, and the linear thermal expansion coefficients of these perovskite crystal films are reduced towards the solid electrolyte layer of the membrane electrode assembly.