The　utilization　of　steel　slag　(SS)　in　the　field　of　concrete　remains　limited　due　to　its　poor　soundness.　This　work　studies　the　long-term　volume　stability　and　strength　development　(up　to　1　year)　of　engineered　cementitious　composites　(ECC)　containing　high-volume　SS.　The　result　shows　that　the　compressive,　splitting-tensile　and　flexural　strength　of　ECC　containing　SS　begins　to　decline　after　90　d,　while　the　decline　in　the　corresponding　matrix　is　much　higher.　Especially,　the　matrix　with　60　wt%　SS　loses　its　integrity　by　360　d.　The　expansion　of　SS　reduces　the　fracture　toughness　of　the　matrix,　leading　to　an　increase　in　toughness　and　ductility,　while　changing　the　cracking　pattern　of　the　ECC.　Additionally,　the　introduction　of　ground　granulated　blast　furnace　slag　(GGBFS)　results　in　a　decrease　in　volume　expansion　and　strength　loss　of　ECC　caused　by　expansion　of　SS.　Randomly　distributed　PVA　fibers　restrict　volume　expansion　of　ECC　containing　SS,　while　trapped　air　pores　introduced　with　PVA　fibers　act　as　relievers,　dispersing　expansive　stress.　Combined　introduction　of　GGBFS　and　PVA　fibers　leads　to　a　49.8　%　reduction　in　expansive　strain　and　a　126　%　increase　in　compressive　strength　of　ECC　compared　with　the　matrix　with　high-volume　SS.