Steel　slag　is　an　industrial　solid　waste,　which　can　provide　a　new　calcium　source　for　microbial　mineralization　as　it　contains　abundant　calcium　elements.　This　study　treated　cemented　backfill　material　with　microorganisms　and　steel　slag　to　enhance　its　performance.　The　influence　of　microbial　treatment　on　the　strength,　microstructure,　and　pore　characteristics　of　the　backfill　was　assessed　using　a　strength　test,　nuclear　magnetic　resonance,　scanning　electron　microscopy,　and　X-ray　diffraction.　The　results　indicate　that　(1)　the　microbial　mineralization　and　the　hydration　reaction　take　place　at　the　same　time;　(2)　when　the　proportion　of　bacterial　solution　exceeded　50%,　microorganisms　excessively　consumed　Ca2+,　which　hindered　the　following　hydration　reaction;　(3)　the　additional　amount　of　bacterial　solution　added　into　the　steel-slag-based　cemented　backfill　material　should　be　less　than　50%,　which　increases　the　strength　by　up　to　22.10%;　(4)　the　excessive　bacterial　solution　sharply　reduces　the　strength　of　the　backfill　even　by　21.41%;　and　(5)　the　addition　of　bacterial　solution　affects　the　pore　characteristics.　A　50%　bacterial　solution　can　make　backfill　reach　its　lowest　porosity.　The　strength　has　an　inversely　proportional　relationship　with　porosity,　diameter,　and　roundness　(σ　=　ax　+　b,　a　©　2024　by　the　authors.