The　effects　of　phosphorus　addition　and　annealing　temperature　on　the　microstructure　and　mechanical　properties　of　equal　atomic　ratio　FeCoCrNiMn　high-entropy　alloys　(HEAs)　were　systematically　studied.　The　phase　composition,　microstructure,　hardness,　and　tensile　properties　were　examined.　The　results　demonstrate　that　the　heterogeneous　structure　consists　of　residual　deformed　grains,　partially　recrystallized　grains,　and　fully　recrystallized　grains,　which　can　be　effectively　tuned　by　increasing　the　P　content.　Furthermore,　the　addition　of　P　delayed　the　recrystallization　of　the　HEAs　because　of　the　precipitation　of　metal　phosphides,　which　hindered　dislocation　movement　and　annihilation.　The　incorporation　of　P　in　HEAs　not　only　avoids　embrittlement　but　also　achieves　excellent　strength-ductility　synergy.　For　cold-rolled　and　annealed　HEAs,　as　the　P　content　increases　from　0　to　0.03　(molar　ratio),　the　yield　strength　is　enhanced　from　392.31　MPa　to　926.64　MPa,　while　the　alloy　retains　a　significant　tensile　ductility　of　approximately　10　%.　Microstructural　analysis　indicated　that　the　increase　in　the　strength　of　the　homogenized　HEAs　is　primarily　due　to　the　strong　solid-solution　effect　of　the　P　atoms.　Based　on　detailed　microstructural　analysis,　it　was　found　that　the　strengthening　mechanism　was　mainly　related　to　the　heterogeneous　deformation-induced　hardening　of　the　heterogeneous　structure.　This　study　demonstrates　that　although　P　is　traditionally　regarded　as　an　embrittlement　element　in　steel,　the　addition　of　an　appropriate　amount　of　P　can　enhance　the　strength-ductility　synergy　in　HEAs.　©　2025　Elsevier　B.V.