Abstract: The mangrove bacterial composition in three intertidal zones (low, mid, high) of Beilun estuary, China was investigated by high throughput DNA pyrosequencing of the 16S rRNA gene. The results demonstrated that bacterial communities in mangrove sediments of Beilun estuary were highly diverse. Shannon index of microbial diversity from the different intertidal zones ranged from 10.2 to 10.4. Phylogenetic analysis showed that bacterial communities from mangrove sediments were dominated by Proteobacteria, followed by Chloroflexi, Bacteroidetes, Planctomycetes and Acidobacteria. Venn diagram of OTUs distribution suggested that bacterial composition from the different intertidal zones displayed a high similarity. However, heat map and ternary plot demonstrated that each intertidal zone was inhabited by specia l dominant bacterial groups. Pyrosequencing also indicated that some potential bacteria from mangrove played an important role in organic pollutant transformation and biogeochemical transformation.