The N₂O production in two nitrogen removal processes treating domestic wastewater was investigated in laboratory-scale aerobic-anoxic sequencing batch reactors (SBRs). Results showed that N₂O emission happened in the aerobic phase rather than in the anoxic phase. During the aerobic phase, the nitrogen conversion to N₂O gas was 27.7% and 36.8% of NH4+‐N loss for conventional biologic N-removal process and short-cut biologic N-removal process. The dissolved N₂O was reduced to N₂ in the anoxic denitrification phase. The N₂O production rate increased with the increasing of nitrite concentration and ceased when NH4+‐N oxidation was terminated. Higher nitrite accumulation resulted in higher N₂O emission in the short-cut nitrogen removal process. Pulse-wise addition of 20 mg NO2-‐N⋅L-1 gave rise to 3-fold of N₂O emission in the conventional N-removal process, while little change happened with 20 mg NO3-‐N⋅L-1 was added to SBR1.