Determining　the　most　favourable　recycle　ratio　is　an　important　item　in　A2/O　process　operational　optimization.　In　this　work,　feeding　with　sewage,　the　effect　of　recycle　ratio　on　nitrogen　removal　when　using　different　influent　nitrogen　loads　was　tested　in　an　A2/O　process,　which　available　capacity　was　52　L.　Experimental　results　showed　that　increasing　the　internal　recycle　ratio　from　0　to　6　produced　a　14.0%　increase　in　nitrogen　removal.　This　increase　was　achieved　by　improving　ρ　(NOx--N)　removal　efficiency　of　10.2%　with　an　increase　in　ρ　(NH4+-N)　removal　efficiency　of　3.8%.　In　order　to　stabilitate　the　effluent　total　nitrogen　concentration　and　reduce　operational　cost,　internal　recycle　ratio　should　be　increasing　with　influent　ρ　(NH4+-N)　loading.　The　optimal　internal　recycle　ratio　is　2　in　general.