<strong>Bioaccumulation of Mercury (Hg) in Seagrass <em>Enhalus acoroides</em> and Mangrove <em>Rhizophora apiculata</em> in Pari Island, Seribu Islands. </strong>Heavy metal pollution, especially Hg metal in Jakarta Bay, is feared to have a negative impact on the quality of the waters around the Jakarta Bay waters, one of which is Pari Island in the Thousand Islands. Seagrass and mangroves plants distributed surrounding Pari Island can be used as indicators of heavy metal pollution. The value of bioaccumulation and translocation of Hg metal factors will provide an overview of the ability of plants to accumulate heavy metals in their surroundings. This study aims to determine the bioaccumulation and translocation of the heavy metal Hg factor in <em>Enhalus acoroides</em> seagrass and <em>Rhizophora apiculata</em> mangroves on Pari Island, Seribu Islands. Seagrass and mangrove samples were taken at five sampling points through purposive sampling. The bioaccumulation value was calculated using the ratio of the metal concentrations in each part of the plant body and sediment. Meanwhile, the translocation factor value was calculated by the ratio of Hg concentration in each part of the plant body (roots/rhizomes, stems, and leaves). The results of this study indicate that the bioaccumulation value in seagrass is infinite (bioaccumulation factor, BAF=∞) and in mangroves is 1.57 (BAF>1). The highest <em>translocation factor</em> value in seagrass leaves is 3.86 (translocation factor, TF) >1) and in mangrove leaves is 2.84 (TF>1). This study shows that seagrass and mangrove plants are classified as good bio accumulator and hyperaccumulator plants and accumulate heavy metals, especially Hg in the upper part of their bodies, namely leaves