In order to explore the effects of oxygen concentration and ammonium content on nitrous oxide emissions from paddy soils, six paddy soils with clay content ranged from 71.0 g/kg to 522 g/kg and pH ranged from 5.23 to 7.83 were collected in China. All soils were incubated at 25℃ and 60% water holding capacity in laboratory after added ammonium at N 10, 30, 50 mg/kg soil and replaced the headspace gases with stock gases which oxygen concentrations were 200 ml/L, 100 ml/L, and 20 ml/L, respectively. The results showed that N₂O emission flux increased with the increase of initial ammonium content but decreased with the increase of oxygen concentration. Stepwise regression analysis indicated that N₂O accumulative emission was positively linearly correlated with the initial ammonium content, soil organic carbon and clay content but negatively with oxygen content (R²=0.845, P<0.01). The negative relationship between N₂O emission and O₂ concentration might be attributed to the increases in N₂O ratio in nitrification products and denitrification rate with the decrease in O₂ concentration. However, the effect of O₂ concentration on the relative contributions of nitrification and denitrification processes to N₂O emissions from paddy soils need to be explored further.