The paper presents the research results of accumulation of Mercury in sediment and two bivalves species: Heamolymph Clam (Meretrix meretrix) and Clam (Corbicula sp.) from Cua Dai estuary, Hoi An city. The average concentration of Hg in sediments is ± μg/g, under allowed limit by the PELS standard (Canada) (≤ μg/g). Content of Hg accumulated in the tissues of Meretrix meretrix is ± μg/g and H is ± μg/g, lower than the allowed standard of the Ministry of Health. Concentration of Hg in sediments and tissues of.