In order to isolate and identify the microbiological strains, which can remove nitrogen, from samples of soil, return sludge of wastewater treatment plants, river water and river sediments and to determine their nitrogen removal activities, this research was performed. The results are summarized as follows: 16 strains which could have denitrification activities were isloated from 36 samples. According to morphological and biochemical results, 14 strains were identified to Pseudomnas sp., and 1 strain to Bacillus sp. and 1 strain to Micrococcus sp.. The strains indentified as Pseudomonas sp., have the high activities of denitrification and degradation of organic compounds, can be used in wastewater treatment plants for the purpose of upgrading the treatment rate. The strians, isloated from this study, grew well at the anoxic state and the average growth rates of cell dry weight per a day were 6.0㎎/ℓ (1st day), 7.0㎎/ℓ (2nd day), l0.0㎎/ℓ (3rd day). Denitrification rates according to incubation day were 40% at Ist day, 60-90% at 2nd day and more than 90% at 3rd day. Removed nitrate nitrogen per cell dry weight was 1.7988gNO₃-N/gMLVSS/day at 1st day, 0.852gNO₃-N/gMLVSS/day at 2nd day, 0.224gNO₃-N/gMLVSS/day at 3rd day. Nitrogen removal activity at 1st and 2nd day was high, but at 3rd day was decreased because of high cell dry weight and low NO₃-N concentration in culture vessel.