The　irreversible　motion　of　magnetic　domain　walls　in　ferromagnets　can　dissipate　a　large　portion　of　the　elastic　energy,　and　the　associated　damping　capacity　is　proportional　to　the　magnetostriction　constant.　In　contrast,　here　we　found　that　the　damping　capacity　of　the　large　magnetostriction　Fe-Ga　alloys　can　be　enhanced　by　2–3　times　through　introducing　structural　defects　including　interfacial　dislocations　and　stacking　faults,　despite　that　these　defects　deteriorate　the　magnetostriction.　These　structural　defects　were　introduced　by　aging　the　BCC　(body-centered-cubic)　solution-treated　precursor,　for　which　the　formation　of　mechanically　harder　FCT　(face-centered-tetragonal)　and　/or　FCC　(face-centered-cubic)　phases　can　result　in　high-density　partial　dislocations　at　the　semi-coherent　phase　interfaces　and　quasi-periodically　stacked　nano-layer　substructure　inside　the　FCC　variants.　The　structural　defects　act　as　extra　damping　sources　besides　the　magnetic　domain　walls　because　the　structural　accommodation　of　the　semi-coherent　phase　interfaces　between　BCC　and　FCT/FCC　nanoprecipitates　with　different　elastic　moduli　and　the　nano-layer　substructure　towards　long-range　ordered　periodical　stacking　can　dissipate　a　large　portion　of　mechanical　energy.　These　findings　suggest　that　introducing　structural　defects　provides　fresh　freedom　to　design　high　damping　ferromagnetic　materials.　©　2021