Sodium salts of ethylene-co-ethyl acrylate-g-maleic anhydride show high rebound resilience, the same as those of both saponified ethylene- co-ethyl acrylates and sodium salts of ethylene-co-methacrylic acids at low salt contents. The measurements of thermal and mechanical properties and dynamic viscoelastic behaviors indicate that the sodium salts of ethylene-co-ethyl acrylate-g-maleic anhydride behave like strong ionic bond cross-linkages close to covalent bond cross-linkages in the polymer, differing from the monocarboxylate salts of saponified ethylene-co-ethyl acrylate and the sodium salts of ethylene-methacrylic acid. It is concluded that the strong cross-linking of the dicarboxylate salts of the neutralized ethylene-co-ethyl acrylate-g-maleic anhydride causes the high rebound resilience.