A high-molecular gelling agent precursor for an electrolyte comprises a copolymer formed of (A) a hydrophobic monomer having a hydrophobic group, which forms a carboxyl group upon saponification, and (B) a hydrophobic polyfunctional monomer. The saponification product of the copolymer has property to gel the electrolyte. A high-molecular gelling agent for the electrolyte is produced by saponifying the precursor with a saponifying agent selected from the group consisting of acids and alkalis while using a reaction medium selected from the group consisting of water and hydrophobic organic solvents.