In　this　study,　an　autotrophic　nitrogen　removal　process　was　established　using　an　integrated　fixed-biofilm　activated　sludge　(IFAS)　reactor　treated　with　high　ammonium　wastewater.　A　nitrogen　removal　rate　(NRR)　of　2.78　kg　N/(m(3).　d)　was　obtained　during　the　206-day　operation.　Moreover,　during　the　stable　period,　the　large　flocs　(D　＞　0.2　mm)　had　a　significantly　higher　abundance　of　anammox　bacteria　than　the　small　flocs　(D　＜　0.2　mm)　and　biofilm,　resulting　in　51%　of　the　anammox　bacteria　being　located　in　the　flocs.　The　result　indicates　that　anammox　bacteria　can　be　enriched　in　the　flocs　and　in　the　biofilm,　which　has　been　rarely　reported　for　IFAS　reactors.　In　addition,　the　large　flocs　are　likely　formed　through　biofilm　detachment　since　the　microbial　community　was　similar　for　the　two　kinds　of　biomass.　Overall,　the　role　of　flocs　in　IFAS　reactors　are　complicated　and　their　contribution　to　the　anammox　reaction　have　been　overlooked　thus　far.