The　purpose　of　this　study　is　to　investigate　the　effect　of　COD/N　interference　on　mature　anammox　granular　sludge　formed　by　different　biological　carriers.　Three　anammox　granular　sludge　rectors　were　established　with　no　biological　carriers　(R1),　GAC　(R2)　and　PVA-gel　bead　(R3),　respectively.　As　the　COD/N　ratio　increased　to　1:2,　the　activity　of　anaerobic　ammonia　oxidizing　bacteria　in　R1　and　R2　was　significantly　inhibited.　However,　the　nitrogen　removal　effect　of　R3　did　not　decrease　dramatically,　and　the　nitrogen　removal　rate　in　this　phase　was　1.54　±　0.05　kg　N/m3·d.　As　the　COD/N　ratio　increased　to　1:1.5,　the　removal　of　NH4　+-N　in　all　reactors　gradually　decreased.　The　order　of　COD　resistance　of　the　three　reactors　in　this　study　was　R3　>　R2　>　R1.　It　was　found　that　Candidatus　Brocadia　might　be　sensitive　to　the　presence　of　organic　matter.　The　abundance　of　heterotrophic　denitrifying　bacteria　increased　gradually　in　each　reactor　under　increased　influent　COD/N　ratios.　©　2020　Elsevier　B.V.