PROBLEM TO BE SOLVED: To provide a polyelectrolyte molding exhibiting excellent proton conductivity even under low humidification condition and low temperature condition, having excellent chemical stability, mechanical strength and fuel barrier properties, and can achieve high output, high energy density, and excellent long term durability in a solid polymer fuel cell, and to provide a solid polymer fuel cell using the same.SOLUTION: A polyelectrolyte composition molding contains an aromatic block copolymer and a cerium compound having one or more hydrophilic segment (A1) containing an ionic group, and a hydrophobic segment (A2) not containing an ionic group. The polyelectrolyte molding forms a co-continuous-like M1 or a lamellar-like M2 phase separation structure, where the cerium content is 0.00015-3 mol% of the ionic group.
