Partial　nitrification-endogenous　denitrification　(PNED)　can　achieve　advanced　nutrient　removal　from　wastewater.　Herein,　an　anaerobic/oxic/anoxic/oxic-sequencing　batch　reactor　(AOAO-SBR)　was　used　to　treat　real　oxytetracycline　(OTC)　pharmaceutical　wastewater　via　PNED.　Partial　nitrification　with　an　average　nitrite　accumulation　ratio　of　91.5　%　was　achieved.　When　the　influent　total　nitrogen　was　105　±　10　mg/L,　the　effluent　of　it　was　only　5.9　mg/L,　and　the　removal　efficiency　was　94.8　%.　In　the　typical　cycle,　multiple　nitrogen　removal　pathways　including　endogenous　denitrification,　simultaneous　nitrification-denitrification,　and　denitrification　contributed　to　68.0　%,　20.3　%,　and　7.3　%.　The　effluent　concentration　of　NH4+-N　was　5　mg/L,　and　NO2−-N　and　NO3−-N　were　not　detected.　The　biodegradation　pathways　of　OTC　were　proposed,　47.1　%　of　OTC　was　degraded　and　eight　possible　degradation　byproducts　were　detected　with　low　toxicity　in　the　extracellular　and　intracellular.　Moreover,　Extracellular　polymeric　substances　increased　from　35.3　(mg/gVSS)　to　74.4　(mg/gVSS)　during　120　days,　which　acts　as　a　critical　role　in　OTC　degradation.　High-throughput　sequencing　results　showed　that　the　relative　abundance　of　ammonia-oxidizing　bacteria　was　2.4　%,　and　nitrite-oxidizing　bacteria　were　washed　out,　which　was　conducive　to　partial　nitrification.　Candidatus_Competibacter　(13.9　%)　enhanced　nitrogen　removal　by　endogenous　denitrification.　Thauera　(13.5　%),　Ottowia　(9.2　%),　and　OLB13　(1.2　%)　are　the　main　OTC-degrading　bacteria.　This　study　provides　a　valuable　reference　to　treat　OTC　pharmaceutical　wastewater　effectively.　©　2025