Steel　slag　(SS)　as　a　supplementary　cementitious　material　has　low　cementitious　activity.　Diethanol-isopropanolamine　(DEIPA)　is　an　organic　admixture　that　can　enhance　the　cementitious　activity　of　cementitious　materials.　This　work　aimed　to　investigate　the　hydration　characteristics　of　SS　under　the　complexing　of　DEIPA.　The　hydration　process　of　SS,　the　complexation　of　DEIPA　with　metal　ions,　and　the　dissolution　process　of　C3A　and　C3S　in　the　presence　of　DEIPA　were　systematically　investigated.　The　results　showed　that　DEIPA　enhanced　the　hydration　of　aluminate　(C3A　and　C12A7),　ferrate　(C2F)　and　silicate　phases　(C3S　and　C2S),　which　formed　a　large　amount　of　monocarboaluminate,　paraalumohydrocalcite　and　C–S–H　gels.　In　the　early　stages　of　hydration,　the　hydration　products　were　mainly　C–S–H　gels,　monocarboaluminate　and　paraalumohydrocalcite,　and　in　the　later　stages　of　hydration,　the　hydration　products　were　mainly　C–S–H　gels,　paraalumohydrocalcite.　The　monocarboaluminate　may　be　transformed　to　paraalumohydrocalcite　at　a　later　stage.　This　hydration-promoting　effect　was　related　to　the　complexation　of　DEIPA.　DEIPA　facilitated　the　dissolution　of　mineral　phases　and　the　precipitation　of　complexed　metal　ions　by　complexing　with　metal　ions.　The　stronger　complexation　of　Al3+　by　DEIPA　made　it　more　solubilizing　for　C3A.　As　a　result,　more　aluminum-containing　hydration　products　were　formed.　The　weaker　complexation　of　Ca2+　by　DEIPA　made　it　a　weaker　solubilizing　for　C3S,　which　also　led　to　a　weaker　promotion　of　silicate　hydration　by　DEIPA.　The　solubilization　of　DEIPA　to　minerals　enhanced　the　cementitious　activity　of　SS,　which　ultimately　led　to　the　increase　in　the　compressive　strength　of　the　hardened　SS　paste　at　each　age.　©　2024　Elsevier　Ltd