TECHNOLOGY FOCUS - POLYMERS - Preparation (Claimed): The sulfonic acid group-containing polymer is obtained by polymerizing a dihydroxy monomer of formula (3) by an aromatic nucleophilic substitution.n=2 or more.Preferred Composition: The sulfonic acid group-containing polymer further has a cyano group-containing structural component of formula (2). The polymer contains a monomer which is a terminal dihydroxy compound of formula (3). The polymer has sulfonic acid group-containing structural unit of formula (4) chosen from 4 claimed groups.n (in formula (2))=same as defined above;n (in formula (3))=1-10;X=-S(=O)2- or C(=O)-, preferably -S(=O)2-;Y=H or univalent positive ion;andZ1=oxygen or sulfur atom, preferably oxygen atom.The content of sulfonic acid group-containing polymer in the resin composition is 50-100 mass%. The fuel cell contains methanol as fuel. The sulfonic acid group-containing polymer has structure of formula (12).X,Y=same as defined above;Z1-Z3=oxygen atom or sulfur atom;Ar1=divalent organic group;Ar2-Ar4=divalent organic group which does not have ionic difference;Ar5=trivalent organic group;andm,n,o=1 or more.Preferred Properties: The sulfonic acid group-containing polymer has sulfonic acid group content of 0.3-5 meq/g and glass transition temperature of 130-270degreesC, preferably 130-220degreesC. EXAMPLE - 3,3'-di-sulfo-4,4'-dichlorodiphenyl sulfone disodium salt (in g) (9.6228), 2,6-dichloro benzonitrile (3.1102), terminal hydroxyl group-containing phenylene ether oligomer (20.71319) and potassium carbonate (5.9873) were mixed in a flask. Subsequently, N-methyl-2-pyrrolidone (100 ml) was added to the flask and heat-stirred at 195-200degreesC for 13 hours. The reaction mixture was cooled, and the polymerization liquid was poured into water, and a sulfonic acid group-containing polyarylene ether-type polymer compound was obtained. The obtained polymer was dried, and the logarithmic viscosity of the polymer was 0.36. A polymeric electrolyte film was formed using a resin composition obtained by dissolving the polymer in N-methyl-2-pyrrolidone. The film had excellent ionic conductivity and durability.