Hampangen Education Forest (HEF) has great potential in terms of carbon stock, biodiversity, and contribution to the local community's livelihood. In the future, it is planned to develop its role in climate change mitigation; thus, valid and updated information regarding climate regulation services are required. The purpose of this study was to assess the above ground biomass (AGB) at different canopy densities of swamp secondary forest in (HEF) and estimated the total AGB stored in this area. The research was carried out from April 2022 until July 2022. The data collected included tree diameter at breast height (DBH), tree total height, the weight of litter, and understorey vegetation. All the information was collected using two types of observation plots (400 m2 and 0.25 m2) and AGB was calculated using allometric equations. This research found that the average AGB at sparse, medium, and dense canopy cover was 70.46 Mg.ha-1, 80.94 Mg.ha-1, and 145.03 Mg. ha-1, respectively. The total AGB stored in HEF was 367,180.08 Mg (tonnes) and equivalent to above-ground carbon stock of 172,574.64 Mg carbon. The finding of this research suggests that HEF needs conservation strategies to improve its carbon stock and conserve biodiversity.