Abstract: Using bromine thymol blue(BTB)identifying medium and the conventional plating method,a strain of aerobic denitrifying bacteria was isolated from a sewage sample from an aeration tank of a Nanjing sewage treatment plant.The strain was named BMB-N6 and was identified as Alcaligenes denitrificans according to the 16S rDNA sequence homology comparison and phyletic evolution analysis.Its denitrifying capacity was determined in media different in nitrite concentration.Optimal denitrifying conditions were explored through orthogonal experiment.The denitrifying capacity of bacterial mixtures of strain BMB-N6 with protein degrading strain BMB-LA,and with ammonia degrading bacteria strain BMB-HKF were determined in both laboratory and field.The denitrifying rate of strain BMB-N6 may reach 94% within 8 h.The optimum denitrifying conditions are rotational speed 50 r·min^-1,C/N 4,pH 6,and 35 ℃.The denitrifying rate of the bacterial mixture may reach 90%(in laboratory within 12 h)and 80%(in field within 7 days).