The invention provides a proton-conducting electrolyte that has excellent proton-conducting properties, heat resistance, and chemical stability without containing any fluorine. The proton-conducting electrolyte contains polyamide sulfamidic acid in which a polyamide backbone has side chains of sulfamidic acid groups. The polyamide sulfamidic acid may be represented by the formula: ##STR00001## where Ar.sup.1 and Ar.sup.2 are each an aromatic ring or a group containing an aromatic ring and n is the average degree of polymerization and is an integer between 100-300,000.