A novel boric acid ester monomer with polymerizable acryloyl group has been designed and synthesized. It is expected that the Lewis acidic nature of this monomer prefers interaction with salts in electrolyte solutions and in polymer gel electrolytes. When the boric acid ester monomer was added to various electrolyte solutions, both of the solubility of salts and ionic conductivity of the solutions were increased considerably. The boric acid ester monomer was polymerized to fix it to the matrix polymer of gel electrolytes. The ionic conductivities of the gel electrolytes increased as compared to those without the boric acid ester monomer. The conductivity enhancement effect was greater for the polymer gel electrolytes than for the electrolyte solutions.