The　N　and　O　isotope　fractionation　effects　in　NO2--N　oxidation　and　nitrification　performance　of　an　activated　sludge　system　treating　municipal　wastewater　are　unknown.　The　nitrifying　sludge　was　cultured　under　different　temperature　(33　+/-　1　degrees　C,　25　+/-　1　degrees　C,and　18　+/-　1　degrees　C)　and　dissolved　oxygen　(DO:　0.5-1　mg/L,　3-4　mg/L,　and　7-8　mg/L).　The　inverse　kinetic　isotope　effects　of　N　and　O　((15)epsilon(NO2)　and　(18)epsilon(NO2))　were　-0.62　parts　per　thousand　to　-7.08　parts　per　thousand　and　-0.87　parts　per　thousand　to　-1.68　parts　per　thousand　in　the　process　of　NO2--N　oxidation,　respectively.　(15)epsilon(NO3)　gradually　increased　with　increasing　of　temperature　((15)epsilon(NO3-33　degrees　C)　(14.49%)　＞　(15)epsilon(NO3-25　degrees　C)　(10.43　parts　per　thousand)　＞　(15)epsilon(NO3-18　degrees　C)　(7.3　parts　per　thousand)),　while　the　(15)epsilon(NO3):(18)epsilon(NO3)　was　maintained　at　1.02-5.32.　The　increase　of　temperature　improved　the　nitrification　activity,　which　promoted　the　fractionation　effect,　but　the　change　of　DO　did　not　highlight　this　difference.　The　exchange　of　NO2--N　and　H2O　(X-NOB)　was　32.5　+/-　1.5%,　and　the　kinetic　isotope　effect　of　H2O　participating　in　the　reaction　((18)epsilon(k),(H2O,2))　was　22.57　+/-　1.79　parts　per　thousand,　indicating　that　H2O　was　involved　in　the　NO2--N　oxidation　rather　than　DO.　In　summary,　the　elevated　temperature　enhanced　the　fractionation　effect　of　NO2--N　oxidation.　This　study　provides　a　new　perspective　to　reveal　the　mechanism　of　NO2--N　oxidation,　optimize　the　process　of　nitrogen　removal　from　wastewater　and　further　control　water　eutrophication.