Large　and　sensitive　magnetostriction　(large　strain　induced　by　small　magnetic　fields)　is　highly　desired　for　applications　of　magnetostrictive　materials.　However,　it　is　difficult　to　simultaneously　improve　magnetostriction　and　reduce　the　switching　field　because　magnetostriction　and　the　switching　field　are　both　proportional　to　the　magnetocrystalline　anisotropy.　To　solve　this　fundamental　challenge,　we　report　that　introducing　tetragonal　nanoprecipitates　into　a　cubic　matrix　can　facilitate　large　and　sensitive　magnetostriction　even　in　random　polycrystals.　As　exhibited　in　a　proof-of-principle　reference,　Fe–Ga　alloys,　the　figure　of　merit—defined　by　the　saturation　magnetostriction　over　the　magnetocrystalline　anisotropy　constant—can　be　enhanced　by　over　5-fold　through　optimum　aging　of　the　solution-treated　precursor.　On　the　one　hand,　the　aging-induced　nanodispersive　face-centered　tetragonal　(FCT)　precipitates　create　local　tetragonal　distortion　of　the　body-centered　cubic　(BCC)　matrix,　substantially　enhancing　the　saturation　magnetostriction　to　be　comparable　to　that　of　single　crystal　materials.　On　the　other　hand,　these　precipitates　randomly　couple　with　the　matrix　at　the　nanoscale,　resulting　in　the　collapse　of　net　magnetocrystalline　anisotropy.　Our　findings　not　only　provide　a　simple　and　feasible　approach　to　enhance　the　magnetostriction　performance　of　random　polycrystalline　ferromagnets　but　also　provide　important　insights　toward　understanding　the　mechanism　of　heterogeneous　magnetostriction.　©　2021,　The　Author(s).