The　exogenous　hydroxylamine　dosing　has　been　proven　to　enhance　nitrite　supply　for　anammox　bacteria.　In　this　study,　exogenous　hydroxylamine　was　fed　into　a　sequencing　batch　reactor　to　investigate　its　long-term　effect　on　anammox　granular　sludge.　The　results　showed　that　hydroxylamine　enhanced　the　reactor＇s　performance　with　an　increase　in　total　nitrogen　removal　rate　from　0.23　to　0.52　kg　N/m3/d　and　an　increase　in　bacterial　activity　from　11.65　to　78.24　mg　N/g　VSS/h.　Meanwhile,　hydroxylamine　promoted　granulation　by　eluting　flocs.　And　higher　anammox　activity　and　granulation　were　supported　by　extracellular　polymeric　substances　(EPS)　characteristics.　Moreover,　Candidatus　Brocadia＇s　abundance　increased　from　1.10　%　to　3.03　%,　and　its　symbiosis　with　heterotrophic　bacteria　was　intensified.　Additionally,　molecular　docking　detailed　the　mechanism　of　the　hydroxylamine　effect.　Overall,　this　study　would　provide　new　insights　into　the　hydroxylamine　dosing　strategy　application.　©　2024