A fuel cell comprising a gas-permeable and electrically conducting support substrate having a fuel gas passage formed therein; a fuel-electrode layer formed on said substrate; a solid electrolytic layer formed on said support substrate so as to cover said fuel-electrode layer and containing ZrO.sub.2 in which rare earth elements are existing in the form of solid solutions; and an oxygen-electrode provided on the solid electrolytic layer so as to face said fuel-electrode layer; wherein said support substrate is formed of a metal of the iron family and/or an oxide of a metal of the iron family, and a rare-earth oxide containing at least one kind of element selected from the group consisting of Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm and Pr. The invention brings a coefficient of thermal expansion of the support substrate close to that of the solid electrolytic layer, and prevents a reduction in the performance of the solid electrolyte caused by the diffusion of elements from the support substrate.