Little information is available on the nitrifying bacteria community in intensive shrimp culture Four experiments were performed to evaluate variations in some bacteria strains (Bacillus, Vibrio, Lactobacillus, Nitrosomonas và Nitrobacter) in the Artemia system applied bio-floc technology. Experiment 1 and 2 were conducted at different salinities (35, 60, 80 and 100?) under laboratory condition and in the fertilization ponds, respectively. Experiment 3 was done in the room conditions with and without aeration conditions and experiment 4 was performed in the Artemia ponds with and without aeration conditions combined with different raking frequencies (1 or 2 times a day). These two experiments were set up at salinity of 80 ppt. Cassava powder and chicken manure were supplemented every three days to maintain the ratio of C:N ? 10: 1. The results of experiment 1 showed that in laboratory experiments, Bacillus and Vibrio appeared at the beginning of the experiment in all salinity treatments. Nitrosomonas and Nitrobacter developed from day 6. The highest density and largest percentage were found for Bacillus, followed by Vibrio, Nitrosomonas and Nitrobacter. Moreover, the densities of Bacillus, Vibrio, Nitrosomonas and Nitrobacter at 35 ppt were significantly