Ca Mau cape alluvial ground is formed from the sediment of the Me Kong river; its soil is fine-sized grain and mostly clay. A total of eleven microorganisms were recorded for this area, of which many groups have an important ecological role in the biogeochemical cycles, such as, Bacillus, Flavobacterium, Pseudomonas, Streptomycetes. The density of microorganisms is high in the area with exposure time from 5-9 hour/day. Among microorganisms, Pseudomonas has the highest density of approximately 3.2 × 108 CFU/g. The diatom communities comprise 23 native frestwater species, 52 brackish water species and 71 marine species. The plant Avicennia sp. is the pioneer in occupying the low-lying land, that creates favorable conditions for sediment capture and form the alluvial areas in the Camau cape. Being followed in ecological succession, mangrove trees form the belts that appeared following the exposure time. Young trees of Avicennia at the area of < 5 hour exposed/day, the mature Avicennia growth at the area of 5-7 hour exposed/day, the mixed trees of Avicennia and Rhizophora growth at the area of 7-9 hour exposed/day and Rhizophora are dominant at the area of over 9 hour exposed/day.