A heterotrophic denitrifying strain named ND1 has been isolated from rotating drum biofilter (RDB) which was mainly used for the treatment of exhaust gas such as NOx. It was proved to be Gram-negative. In addition, it was able to form dry and wrinkled colonies on the medium, adhere on the agar surface, produce yellow pigments and be motile with a single polar flagellum. It was indentified as the Pseudomonas stutzeri according to morphological and physiological biochemical characteristics and 16S rDNA sequence analysis. Under the conditions of pH 7.2 and temperature 30 degrees C, the NO3- -N removal efficiency by ND1 was up to 100% in 5 days,while the NO2- -N degradation ratio was only 85% by the strain DN1 when subjected to the same condition as the above.