This study aimed to calculate the economic value of carbon in the mangrove ecosystem of Cawan Island Indragiri Regency, Riau, Indonesia. Mangrove data retrieval was carried out at three stations using the 10 x 10 m quadratic transect method. A non-destructive sampling method used to estimate tree biomass, by measuring all diameters at breast height (DBH=1.3 m) of mangroves, then calculating using an allometric model. The types of mangroves found on Cawan Island are Rhizophora mucronata, Rhizophora apiculata, Xylocarpus granatum, Sonneratia alba, Sonneratia ovata, Lumnitzera racemosa, Bruguiera gymnorrhiza and Nypa fruticans. Rhizophora apiculata has the highest biomass of 2,207.48 tons.ha-1 with a carbon potential of 1,015.43 tons-C.ha-1 and carbon absorption of 3,723.24 tons-CO2.ha-1, in general, Cawan Island mangroves have a biomass value of 4,838.40 tons.ha-1 with a carbon potential of 2,199.54 tons-CO2.ha-1 and carbon absorption of 8,064.98 tons-CO2.ha-1. The total value of carbon sequestration produced by mangroves on Cawan Island is IDR.598,566,978,912.year-1.