Abstract: The rate of above ground carbon sequestration was examined in mangrove forest filtration system pond within the King’s Royally Initiated Laem Phak Bia Environmental Research and Development Project that located in Thailand. It is divided into two sites: the study site and the reference site. The study site is the mangrove filtration system area where is directly affected from the municipal waste water and the reference site is the mangrove forest area where is indirectly affected from the municipal wastewater at Ban Pranaen is located in the north of the cape. The relationships between tree diameter and tree height were used to evaluate above ground biomass by allometric equations and above ground carbon sequestration was calculated by multiplying the percentage of carbon stock. They were carried out two seasons: Wet and dry seasons. The results were revealed that the highest LAI in study site and reference site were 17.67 and 9.66, respectively. The highest above ground biomass was 1.42 and 2.12 t ha-1 in study site and reference site, respectively. The percentage of carbon content in the parts of sampled tree was slightly difference in study and reference site. The average of highest above ground carbon sequestration was 11.08 and 2.32 t ha-1 in study site and reference site, respectively. Moreover, the results of comparison of LAI, above ground biomass and above ground carbon sequestration confirmed that the mangrove forest filtration system can be high potential of carbon stock source.