TECHNOLOGY FOCUS - POLYMERS - Preferred Composition : The aromatic polymer has constituent units represented by general formula (1) and/or (2).Z1 = C=O or O=S=O ;m = 0, 1 or 2 ;n = 0 or 1 ;Z2 = C=O or O=S=O ;Ar1, Ar2 = divalent aromatic groupsTypical units constituting the aromatic polymer are represented by general formula (3) and/or (4). The aromatic polymer is preferably an aromatic polyether ketone containing a constituent group represented by general formula (5) and also a cation exchange group. The aromatic polymer is an aromatic polyether sulfone block copolymer, an aromatic polyether ketone block copolymer or a mixture of these, which comprise a hydrophilic segment containing cation exchange groups and a hydrophobic segment containing no cation exchange groups. The hydrophobic segment comprises a constituent unit represented by general formula (6). The hydrophilic segment comprises a constituent unit represented by general formula (7), in which all or a part of the aromatic residue groups are substituted with cation exchange groups.Z3, Z4 = C=O or O=S=O ;p, q = integers between 3 and 1500 ;Ar4 = divalent aromatic group which bonds with electrophyllic groupsThe fused salt contains the ammonium ion as a cation component. The amount of the fused salts contained in the composition is 3 - 90 wt%. The cation exchange group is a sulfonic acid or carboxylic acid group. Preferred Process : A process for producing the polyelectrolyte composition comprises dissolving a specific amount of the aromatic polymer and a specific amount of the fused salt in a solvent which can dissolve both substances, and then removing the solvent by drying. WIDER DISCLOSURE - A polyelectrolyte membrane comprises the invented polyelectrolyte composition.    EXAMPLE - N-ethylimidazole trifluoromethane sulfonate was produced by adding dropwise trifluoromethane sulfonate to an ethanol solution containing N- ethylimidazle at 0 degreesC, stirring the mixture at RT and removing the ethanol. An aromatic polyether sulfo random copolymer containing sulfonic acid, and the above N-ethylimidazole trifluoromethane sulfonate were dissolved in N, N- dimethylacetoamide. The solution was made to flow on a glass plate, dried at 60 degreesC for 5 hours and at 120 degreesC in vacuum for 16 hours so as to obtain a transparent film. The film had an ion-conductivity of 2 x 10-2 S cm-1 even in the absence of water or a solvent.