A method for mounting a seal in a fuel cell comprising: a membrane electrode assembly formed by holding an electrolyte membrane between a first electrode and a second electrode and having a seal mounting portion; a separator plate layered on both surfaces of the membrane electrode assembly so as to form gas passage; and a frame-shaped separator plate held between the membrane electrode assembly and the separator plate so as to seal the gas passage in air tight. The method comprises: preforming the seal into a predetermined shape; setting the seal at the mounting portion of the membrane electrode assembly; and integrally forming the seal with the membrane electrode assembly.