Abstract: The experiments investigated the production of N₂O under different ρ(C)/ρ(N) during denitrification using nitrification treated wastewater in SBR.Different ρ(C)/ρ(N),which were 0、1.2、3.5、5.0 and 20,respectively were used.The results showed that the production of N₂O using endogenic carbon resource was small and the denitrification rate was only 10%.Under the ρ(C)/ρ(N) 1.2 and 2.4 condition,the production of N₂O were also small and the denitrification rates were 18.44% and 33.55%,respectively.When the ρ(C)/ρ(N) were 3.5 and 5.0,the denitrification rates were 71% and 91.4% and the production of N₂O were 0.227mg/L and 0.135mg/L,respectively.They were 30 and 18 times higher than that using endogenic carbon source process.Increasing the ρ(C)/ρ(N) to 20,the denitrification rate was 99.29% and the production of N₂O was 0.317mg/L.Consequently,the denitrification process could produce fewer N₂O,but it severely affected the denitrification effect.To reach a high denitrification rate,it was necessary to increase the ρ(C)/ρ(N),but production N₂O also increased.Therefore,in the denitrification process,it suggests that limiting the ratio of ρ(C)/ρ(N) around 5 can achieve good denitrification performance and produce fewer N₂O.