A　denitrifying　ammonium　oxidation　(DEAMOX)　process　has　been　regarded　as　an　innovative　process　to　simultaneously　treat　ammonia　and　nitrate　containing　wastewaters,　whereas　very　limited　research　has　focused　on　its　application　in　biofilm　system.　In　this　research,　a　novel　DEAMOX　process　was　established　with　fixed　sponge　carriers　in　a　sequencing　biofilm　batch　reactor　(SBBR).　To　investigate　biofilm　formation　process　and　characteristics　can　encourage　further　research　on　DEAMOX　system　optimization,　deteriorated　performance　recovery　strategies　and　application　with　actual　wastewater.　Total　nitrogen　removal　efficiency　was　maintained　at　93.0　%　after　240　days　of　operation.　With　biofilm　growth,　the　protein-like　extracellular　polymeric　substances　(EPS)　and　tightly-bound　EPS　(TB-EPS)　of　biofilms　increased　from　65.6　to　46.1,　to　179.6　and　142.0　mg　gVSS(-1),　respectively,　revealing　that　protein-like　substances　and　TB-EPS　promote　biofilm　formation.　The　mechanism　of　biofilm　formation　was　discussed　by　analyzing　the　morphological　development　and　functional　bacterial　activities　of　biofilms.　Furthermore,　high　anammox　activity　was　obtained　in　biofilms　with　specific　NH4+-N　removal　rates　over　4.29　mgN　gVSS(-1)h(-1),　which　were　significantly　higher　than　in　suspended　sludge　(2.56　mgN　gvss(-1)h(-1)).　Quantitative　polymerase　chain　reaction　results　showed　that　the　abundance　of　anammox　bacteria　in　biofilms　increased　from　1.87　%　to　11.48　%　with　biofilm　growth.　These　results　imply　that　mature　biofilms　formed　on　carriers　and　the　anammox　bacteria　were　sufficient　enriched　in　DEAMOX-SBBR　system.　(C)　2018,　The　Society　for　Biotechnology,　Japan.　All　rights　reserved.