Global climate change can increase carbon dioxide (CO2) emissions in the environment. The mangrove ecosystem is one of the main ecosystems that have a role in mitigating climate change as carbon sinks and stores. Mangroves absorb CO2 during photosynthesis, then convert it into carbohydrates by storing it in biomass. This study aims to determine the mangrove ecosystem’s total biomass, carbon stock, and CO2 sequestration in Anambas islands marine tourism park. The novelty of this research is conducted in conservation areas with minimal potential for land loss so that they can be used as monitoring in the following years. In addition, carbon stock assessment is carried out using allometric equations to obtain Above Ground Biomass (AGB) and Below Ground Biomass (BGB) values so as not to damage the existing mangrove ecosystem. The assessment of total biomass and carbon stock was carried out at 12 stations around Siantan and Jemaja islands using the line transect method. The species of mangrove and diameter breast high (DBH) were measured in each plot with a transect size of 10x10 m. The biomass calculation was carried out to provide information on carbon stock and converted it to get the data of Carbon stocks and estimates of CO2 sequestration. The results showed that the mangrove ecosystem in the Anambas Islands Marine Tourism Park has a biomass of 574.73 tons/ha, an estimated carbon stock of 270.12 ton/ha, and CO2 sequestration of 990.45 ton/ha. The mangrove ecosystem spread over the Anambas Islands Marine Tourism Park is 766.32 Ha, so that it can store carbon reserves of 206,998.39 Ton C. As a conservation area, it is necessary to be sustainably managed to protect the existence of the mangrove ecosystem and increase the carbon stock in the future. Climate change mitigation may be achieved by reducing carbon emission levels and maintaining the mangrove ecosystem services as carbon sinks and sequestration.