Under　hydraulic　retention　time　(HRT)　of　2　h,　A/O　alternating　interval　of　48h,　temperature　of　23~27,　dissolved　oxygen　concentration　(DO)　of　0.2~0.5　mg/L　in　anaerobic　stage　and　3~5　mg/L　in　aerobic　stage,　two　steel　slag　media　biological　filters　(SSMBFs)　were　carried　out　and　operated　in　alternating　anaerobic/aerobic　(A/O)　mode　to　investigate　characteristics　of　nitrogen　and　phosphorus　removal　from　artificially　synthesized　domestic　wastewater　with　influent　quality　of　pH　6.8~7.5,　COD　260~330　mg/L,　NH4+-N　35~40　mg/L　and　PO43--P　9~11　mg/L.　The　results　showed　that　the　alternating　A/O-SSMBFs　performed　a　promising　performance　for　wastewater　treatment,　as　well　as　the　NH4+-N,　PO43--P　and　COD　could　be　removed　more　than　95%,　40%~60%　and　83.3%　respectively,　and　the　effluent　concentrations　of　NH4+-N,　PO43--P　and　COD　decreased　to　0.5　mg/L,　3~6　mg/L　and　50　mg/L　respectively.　It　was　also　observed　that　the　biological　activity　of　ammonia　oxidizing　bacteria　(AOB)　and　phosphorus　accumulating　bacteria　(PAOs)　could　be　recovered　in　10　hours　and　8　hours　respectively,　while　the　SSMBF　alternating　converted　operational　mode　every　48h　from　anaerobic　to　aerobic　or　on　the　contrary.　The　SEM　and　EDS　characterization　of　crystals　formed　on　the　media　surface　and　analysis　of　pollution　removal　character　revealed　that　the　phosphorus　in　an　alternating　A/O-SSMBFs　system　could　be　removed　by　both　biological　oxidization　and　crystallization.　Because　the　steel　slag　media　could　release　alkalinity　and　ion　as　well　as　the　PAOs　could　release　phosphorus　under　the　anaerobic　environment,　the　phosphorus　removal　by　crystallization　had　been　enhanced　in　this　system.　The　principal　constituent　of　crystalline　substance　was　hydroxyapatite.　©,　2015,　Chinese　Society　for　Environmental　Sciences.　All　right　reserved.