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In order to study the concentration of heavy metals in important rivers in the southern part of the Caspian Sea, samples were collected in three upstream points, estuary and depth of 1 to 10 m of the sea, a surface sediment sample and a core sample. Granulation analysis, organic matter assay, and determination of heavy metal concentrations were performed on each sample. The highest concentrations of iron (45000 ppm), aluminum (74000 ppm), chromium (142.78 ppm), cobalt (33.67 ppm) and lead (56.70 ppm) in Ramsar, arsenic (18.45 ppm) and Zinc (110.3 ppm) was observed in Gorganrood river, nickel (60 ppm) in Qarahsu river and copper (52.63 ppm) in Sefidrood. Moreover, the lowest concentration of elements in the core of Gorgan Bay (K5) and a depth of 85 cm with an approximate age of 1400 years was obtained, which was used as the baseline reference. Based on the contamination degree (Cd) index, three rivers of Babolrood, Cheshmeh Kileh and Sardabroud were classified in the range of moderate contamination and Gorganrood, Qarahsoo, Tajan, Ramsar and Sefidrood rivers were classified in the area of ​​significant contamination. Based on the modified contamination degree index (mCd), all rivers were in the range of low to medium contamination degree, and pollution load index (PLI) was in the range of more than 1 (slightly polluted to polluted) at most stations. In terms of ecological risk index (RI), rivers were in the low-risk range. Enrichment index (EF) in sediments of estuarine sections showed that the rivers are probably enriched by various factors such as geology, climatic conditions, and human factors having moderate to severe pollution.