The composition of bacterial community in the Alexandrium tamarense culture was determined by analyzing the 16S rDNA clone libraries. 16S rRNA gene was amplified by using the total DNA extracted from the A. tamarense culture at three growth stages as templates. 34 different restriction fragment length polymorphism (RFLP) patterns of the clones were obtained from the three libraries. Clones representing each RFLP patterns were sequenced and phylogenetic analysis revealed that the Proteobacteria and the Bacteroidetes group can be the dominant component in the phycosphere microflora. Results showed that in the lag phase, alpha-Proteobacteria (36.4%), gamma-Proteobacteria (27.3%) and Bacteroidetes (27.3%) were the dominant group; in the late-exponential phase, the clones belonged to alpha-Proteobacteria (53.3%), beta-Proteobacteria (13.3%), gamma-Proteobacteria (6.7%), and Bacteroidetes (26.7%); and in the stationary phase, the community was comprised of alpha-Proteobacteria (47.8%), beta-Proteobacteria (8.7%), gamma-Proteobacteria (21.7%), delta-Proteobacteria (4.3%) and Bacteroidetes (17.4%). The results also suggest that a part of the bacteria associated with A. tamarense are uncultured and novel species. And these bacteria may play a major role in regulating the processes of algal bloom initiation, maintenance and decline. So these results may provide us great academic and practical importance in controlling the algal blooms by microbes.