A slight halophilic heterotrophic nitrobacteria named gs1 was separated from the matured activated sludge. According to the morphological observation, physiological biochemical tests and sequence analysis of the 16S rDNA, strain gs1 was identified to be as Pseudomonas sp. Sodium acetate and ammonium chloride were used as carbon and nitrogen sources, respectively, to investigate the characteristics of the bacterium. When cultured for 24 h under aerobic conditions, with the removal rates of the NH4 +-N and COD being 82.2% and 74.73%, respectively, strain gs1 will have a nitrification function of producing NO2 −-N. When cultured for 24 h under aerobic conditions in nitrite medium, the removal rate of the NO2 −-N became 100%, and when cultured for 24 h under aerobic conditions in nitrate medium, the removal rate of the NO3 −-N became 97%. The result shows that this strain functions for either nitrification or denitrification, i.e., it can complete the full process of biological deoxidation.