Provided are: an acid-type sulfonate group-containing polymer that has excellent hydrogen gas barrier properties and hot water resistance and that generates less oligomer during production; a liquid composition and a solid polymer electrolyte membrane including the acid-type sulfonate group-containing polymer; and a membrane electrode joint body and a solid polymer fuel cell provided with the solid polymer electrolyte membrane. This acid-type sulfonate group-containing polymer has a perfluoromonomer unit, has no monomer unit having a halogen atom other than a fluorine atom, and has an acid-type sulfonate group, wherein: the hydrogen gas permeability coefficient under a condition of a temperature of 80°C and a relative humidity of 10% is less than or equal to 2.5×10-9cm3∙cm/(s∙cm2∙cmHg); the mass decrease rate when being immersed in hot water for 24 hours at 120°C is less than or equal to 15 mass%; and the capacity flow rate value of a polymer having a fluorosulfonyl group which is a precursor of a polymer having the acid-type sulfonate group is greater than or equal to 220°C.
展开▼
