Hydrogels　with　high　strength　and　ductility　are　normally　prepared　from　synthetic　polymers,　and　most　protein-based　hydrogels　are　soft　and　brittle.　Here,　a　strong,　ductile　gelatin　hydrogel　is　prepared　by　simply　soaking　a　virgin　gelatin　gel　in　an　ammonium　sulfate　solution.　The　polymer　chains　in　the　covalent,　crosslink-free　network　can　freely　move　to　homogeneously　distribute　stress,　and　more　importantly,　the　highly　kosmotropic　ammonium　sulfate　ions　greatly　enhance　the　hydrophobic　interactions　and　chain　bundling　within　the　gelatin　gels.　As　a　result,　the　treated　hydrogels　have　an　extraordinary　ultimate　strength　(compressive　and　tensile　strains　of　over　99%　and　500%,　respectively,　and　stresses　of　12　and　3　MPa)　superior　to　that　of　common　protein　gels.　The　physical　crosslinks　introduced　by　the　Hofmeister　effect　can　rapidly　absorb　energy　and　sustain　large　deformations　via　decrosslinking　and　dissociation,　which　result　in　energy　dissipation　and　antifatigue　properties.　The　effects　of　the　gelatin　and　(NH4)(2)SO4　concentrations　on　the　hydrogel　mechanics　are　evaluated,　and　the　possible　strengthening　mechanism　is　discussed.　The　effect　of　various　ions　in　the　Hofmeister　series　on　the　gelatin　hydrogel　is　also　investigated.　Kosmotropic　ions　enhance　the　mechanical　properties,　whereas　chaotropic　ions　soften　and　dissolve　the　gel.