Abstract: We had monitored and investigated the bacterial community composition in aquaculture water for Crassostrea ariakensis in Guandu of Zhanjiang by denaturing gradient gel electrophoresis (DGGE) from March to December, 2011. UPGMA clustering analysis shows that there are 2 major populations of bacterial species. Diversity index reveals that the diversities in March~July were higher than those in August~December. Phylogenetic analysis indicates that the dominant microbial populations in the water are uncultured Proteobacteria (α, γ, δ and ε), uncultured Bacterioidetes, uncultured Verrucomicrobiae bacterium, uncultured Actinobacteria and uncultured Cyanobacter bacterium. Uncultured α-proteobacterium and Flevobacterium of uncultured Bacteroidetes are the most dominant bacteria.