Abstract: Using sequencing batch reactor (SBR), with KNO₃ as nitrogen source, two strains of aerobic denitrifiers were isolated, coded as X₁ and X₂. Their denitrifying activities and yield of N₂O during aerobic denitrification were studied. It is indicated that denitrification could be carried out using nitrate during fully aerobic state (DO＞2mg/L) by aerobic denitrifiers X₁ and X₂. Total inorganic nitrogen removal rate (η_TIN) could be reached to 72.1% and 78.9%, respectively. There was nitrite accumulation during biodenitrification for X₁. When nitrite KNO₂ was used as nitrogen source, η_TIN was only 16% for X₁, but that of X₂ reached to 73%. There was much less N₂O emission for X₂ than X₁ during aerobic denitrification, since the yield of N₂O was related to the accumulation of nitrite. Carbon resource affected greatly to the yield of N₂O. N₂O emission was the highest when sodium succinate was used as carbon resource.