Mangroves play a role in adapting and mitigating climate change through their sedimentation process by capturing and sequestering carbon (termed blue carbon). Indonesia has 2.9 million hectares of mangroves with a total storage of 3.14 billion tonnes of carbon in mangrove forests, making Indonesia one of the potential contributors of blue carbon. This study determines carbon stock (Corg) and sediment accumulation rate (SAR) to find the carbon accumulation rate (CAR) in sediment mangroves at Ujung Kulon National Park. Sampling was taken in 3 locations perpendicular to the shoreline : interior, fringe, and mudflat. The result shows that the interior area has the highest CAR (31.94 ± 3.6 g C m-2 yr-1) even though the carbon stock (90.19 Mg C ha-1) is the lowest from the other two. On the contrary, mudflat, which has the highest carbon stock (169.6 Mg C ha-1), shows the lowest CAR (17.03 ± 5.21 g C m-2 yr-1). This indicates that geomorphic differences are one of the causes of variations in CAR