The objective of the study is to calculate carbon accumulation of mangrove tree (Rhizophora apiculata) on the three different mangrove forest types at elevation in the mangrove ecosystem at Ngoc Hien district, Ca Mau province as the basis for the recommendations of environmental service calculation. The carbon accumulation of standing trees was calculated from biomass of tree. The biomass data were calculated through the correlation equation between diameter at breast height (DBH) and tree biomass [1] on 18 plots for three different mangrove types. Soil samples in each plot were collected to evaluate the correlation between environmental conditions and carbon accumulation. The results showed that the total biomass for all species was decreased from the fringe mangrove to estuarine mangrove and then the lowest biomass was found at riverine mangrove. However, carbon accumulation of the mangrove trees (Rhizophora apiculata) was decreased from the fringe mangrove (62.1 tonhectare^-1) to riverine mangrove (57.4 tonhectare^-1), and the lowest was in estuarine mangroves (44.2 tonhectare^-1). The result showed that there was statistically significant difference significant among three types mangrove about biomass and C accumulation. In addition, there was a positive relation between biomass with elevation and Eh.