Marine bivalves are aquatic organisms commonly found in the intertidal zone that frequently exposed to pollution and anthropogenic activities. The study aimed to determine the bivalvian diversity and its distribution pattern in Belawan Waters as one of the most polluted estuary area in North Sumatra. The study used purposive sampling in two sites, Station-1 was located at the mangrove forest in Kwala Besar and Station-2 was located at Bagan Belawan or human-exposed waters. The study documented seven species of bivalves with Solen sp. as the most abundant species (3.33 ind/m2) at Site-1 and Hiatula chinensis (7.44 ind/m2) at Site-2. The Shannon’s diversity index (H’) of bivalves in Belawan Waters was categorized as low level of divesity in both sites. The distribution pattern of Atrina pectinata, Lingula anatina, and Placuna sp. was randomly distributed while Anadara granosa, Solen sp., Hiatula chinensis and Tellina exerythra was clumped in the area based on the Morisita’s index. Bivalve diversity index was positively correlated with the physicochemical characteristics of Belawan waters, including pH, COD, TSS, and PO4, while TDS, BOD5, DO, Substrate Organic Content, salinity, and temperature were negatively correlated to the diversity.