To provide a liquid composition capable of forming a membrane excellent in durability against hydrogen peroxide or peroxide radicals and excellent in hydrogen gas barrier property; a polymer electrolyte membrane; a membrane electrode assembly; and a polymer electrolyte fuel cell.Liquid composition comprising a liquid medium, an acid-type sulfonic acid group-containing fluorocarbon polymer of which the hydrogen gas permeation coefficient under the conditions of a temperature of 80°C and a relative humidity of 10% is at most 2.5 × 10^-9 cm³·cm/(s·cm²·cmHg), and cerium atoms; a polymer electrolyte membrane 15 comprising the acid-type sulfonic acid group-containing fluorocarbon polymer, and cerium atoms; and a membrane electrode assembly 10 comprising an anode 13 having a catalyst layer, a cathode 14 having a catalyst layer, and the polymer electrolyte membrane 15 disposed between the anode 13 and the cathode 14.