To　investigate　the　influence　of　different　sizes　of　ettringite　on　the　early　strength　performance　of　foundry　sand,　various　sizes　of　ettringite　(AFt-0,　AFt-1,　and　AFt-2)　were　first　prepared　using　different　dispersants.　The　prepared　series　of　AFt　were　characterized　by　FTIR,　XRD,　and　SEM.　Comparative　analyses　were　conducted　on　the　mechanical　properties,　microscopic　morphology,　hydration　heat　of　cement,　and　setting　time　of　foundry　sand　using　different　analytical　methods　to　assess　the　effects　of　various　sizes　of　ettringite　on　the　foundry　sand.　The　results　show　that　adding　dispersants　could　control　the　size　of　ettringite　and　improve　its　suspension　stability　in　solution.　The　addition　of　ettringite　of　different　sizes　could　enhance　the　early　compressive　strength　of　foundry　sand,　with　a　greater　increase　observed　as　the　size　of　ettringite　decreases.　Specifically,　incorporating　AFt-2　into　the　foundry　sand　increases　the　compressive　strength　by　225%　compared　to　the　blank　sample　at　the　same　age,　approaching　the　compressive　strength　of　the　blank　sample　at　1　d.　Microscopic　structural　analysis　of　the　foundry　sand　also　reveals　that　with　decreasing　ettringite　size,　the　early　formation　of　ettringite　in　the　foundry　sand　increases,　which　facilitates　the　formation　of　an　early　skeleton　system　in　the　foundry　sand.　Hydration　heat　analysis　further　indicates　that　as　the　size　of　ettringite　decreases,　the　rate　of　cement　hydration　accelerates,　leading　to　a　shorter　cement　setting　time.　©　2025　Beijing　University　of　Aeronautics　and　Astronautics　(BUAA).　All　rights　reserved.