Abstract:［Objective］We obtained an alkali-tolerant denitrifying bacterium，and determined its denitrifying activity and alkali-tolerance． ［Methods］An alkali-tolerant denitrifying bacterial strain was obtained by isolation and purification．We identified the bacterial strain by morphological observation，physiological test and 16S rRNA analysis． We determined the denitrifying activity and alkali-tolerance by effects of initial nitrate concentration and initial pH on denitrification．［Results］An alkali-tolerant denitrifier strain R9 was isolated from the lab-scale high-rate denitrifying reactor，and it was identified as Diaphorobater nitroreducens． The strain R9 grew heterotrophically with methanol as the electron donor and nitrate as the electron acceptor．The nitrate conversion was 93. 25% when strain R9 was cultivated for 288 h with initial nitrate concentration 50 mg/L and initial pH 9.0．The denitrification activity could be inhibited at high nitrate concentration with a half inhibition constant of 202.73 mg N/L．Strain R9 showed a good alkali tolerance with the nitrate removal rate at pH 11.0 remained 86% of that at pH 9.0．［Conclusion］ Strain R9 was identified as Diaphorobater nitroreducens，and it was an alkali-tolerant denitrifying bacterium with optimum pH value of 9.0.