Arsenic contamination in water bodies and associated health hazards has become an important environmental issue. In this study, the total arsenic concentrations in surface sediments as well as clams and the arsenic species (arsenite (As(Ⅲ)), arsenate (As(Ⅴ)), monomethylarsonate (MMA), dimethylarsinate (DMA) and arsenobetaine (AsB)) in clams from the main estuaries of Lake Dongting were investigated. Meanwhile, both the potential ecological risk of arsenic in surface sediments and the health risk of eating clams were assessed. The results showed that the total arsenic concentrations in surface sediments were 11.47-61.20 mg/kg, and the horizontal distribution pattern of arsenic was as follows:South Lake Dongting > East Lake Dongting > West Lake Dongting. The total arsenic concentrations in clams were 6.36-11.15 mg/kg, and no significant difference was found among sampling sites. The arsenic species distribution in the clams was AsB > As(Ⅴ) > DMA > As(Ⅲ) > MMA. The Hakanson potential ecological risk index (E_r) was applied for assessing the extent of potential ecological risk of arsenic in surface sediments. The average of E_r was 23.09, indicating that the potential ecological risk of arsenic in surface sediments belonged to low level. Meanwhile, both the carcinogenic risk (CR) and hazard quotient (HQ) were used to assess the potential health risks of human dietary exposure to inorganic arsenic (iAs) through clam. The CR_iAs values reached 1.36×10^-3-3.43×10^-3, and the mean value was 2.24×10^-3, of which all exceeded the upper limit of USEPA's acceptable risk range (1×10^-4). The HQ_iAs values also reached 3.01-7.61, and the average of HQ_iAs was 4.98, which was 5 times of standard value. It was suggested that long-term intake of native clam from the main estuaries of Lake Dongting was associated with increased both carcinogenic and non-carcinogenic health risk. The results of this study are of great significance for understanding the status and risk level of arsenic contamination from surface sediments and benthos in the main estuaries of Lake Dongting, and provide scientific basis for the control and treatment of arsenic contamination in this basin.