Nitrous　oxide　production　in　different　influent　COD/N　ratios　was　investigated　in　lab-scale　batch　reactors　using　nitrite　and　nitrate　as　different　electron　acceptors,　adding　ethanol　as　external　carbon　source.　The　results　showed　that　the　maximum　production　of　N2O　was　1.91%　(nitrite)　and　0.48%　(nitrate)　of　influent　nitrogen,　whereas　0.22%　(nitrite)　and　0.31%　(nitrate)　in　the　optimal　influent　COD/N　ratio.　Taking　the　effluent　water　quality　and　the　minimum　N2O　production　into　account,　the　experiments　suggested　that　the　optimal　influent　COD/N　ratio　was　2.7-4.3　(nitrite)　and　5.2-6.8　(nitrate).　Furthermore,　the　results　also　demonstrated　that　the　limited　availability　of　electron　donor　resulted　in　nitrite　accumulation　which　leaded　to　high　N2O　production.　Hence,　In　order　to　reduce　the　production　of　N2O,　it＇s　important　to　control　influent　COD/N　ratio　in　an　optimal　value　to　avoid　the　accumulation　of　nitrite.