An aerobic denitrifying bacterium DN7 was isolated from the bio-contact oxidation reactor treating bamboo processing wastewater. Cellular morphology demonstrated that strain DN7 was a gram negative bacillus with an average size of 0.5 μm×1.5 μm and the colony was ivory. Based on the homologic analysis of the 16S rDNA sequence and physiochemical properties, the strain was identified as Defluvibacter lusatiensis str.. The denitrification characteristics of strain DN7 with different sources of nitrogen were investigated. Results showed that the strain could use either nitrate or nitrite as the sole source of nitrogen for aerobic denitrification, and the removal efficiencies of nitrate and nitrite were 83.35% and 85.72% in 4 h, respectively. The completely reduction of nitrite was 42 h before the nitrate. Almost no nitrite accumulation was observed in the aerobic denitrification process with nitrate as the sole nitrogen source, whereas nitrate accumulation was detected with nitrite as the sole nitrogen source, in which the maximum amount of nitrate reached 21.83 mg/L in 4 h. The strain preferred nitrate to nitrite in the nitrate-nitrite mixed system. Coexistence of nitrite and nitrate had no significant effect on nitrate reduction, however, the residual concentration of nitrite increased with the ratio of nitrite to nitrate. As the ratio of nitrite to nitrate increased from 1∶9 to 5∶5, the residual nitrite concentration increased from 3.38 mg/L to 7.60 mg/L. Little amount of nitrate would inhibit the nitrite reduction significantly. When the ratio of nitrate to nitrite was 1∶9, the nitrite removal efficiency dropped to 74.79%, much lower than that with nitrite as the sole nitrogen source. The strain was capable of using ammonium nitrogen as the sole nitrogen source, in which both heterotrophic nitrification and aerobic denitrification occurred. Nitrate accumulation was observed in the heterotrophic nitrification and aerobic denitrification process, and the maximum value was 18.92 mg/L. In 72 h, the removal efficiency of ammonium nitrogen reached 85.66%, and neither nitrate nor nitrite accumulation was observed. The aerobic denitrification of the strain could be promoted in the presence of little amount of ammonium nitrogen. When the ammonium to nitrate ratio was 1∶9, nitrate was completely reduced in 48 h, 24 h before that with nitrate as the sole nitrogen source. Coexistence of nitrate and ammonium nitrogen also enhanced the heterotrophic nitrification. When the nitrate to ammonium ratio was 1∶9, removal efficiency of ammonium nitrogen reached 87.50%, 7.05% higher than that with ammonium nitrogen as the sole nitrogen source.