Objective To characterize methylmercury (MeHg) bioaccessibility from commonly consumed species of marine fish in Guangdong Province, and to investigate the effects of bioaccessibility on MeHg exposure of dietary marine fish. Methods A total of 36 samples of 12 species of marine fish were purchased from seafood trading market in Guangzhou City. The bioaccessibility of MeHg from raw, fried, grilled and steamed fish samples was determined by dual-phase in vitro gastrointestinal digestion based on the physiologically based extraction test. The bioavailability of MeHg in different sea fish and cooking method was compared, and bioaccessibility-corrected MeHg exposure assessment was conducted. Results The bioaccessibility of MeHg from raw fish ranged from 26.5% (Trichiurus lepturus) to 84.3% (Cynoglossus). Frying and grilling reduced MeHg bioaccessibility by 29.0% and 30.7% (P＜0.05), respectively. There was no significant change after steaming (P＞0.05). A significantly negative correlation was observed between initial MeHg concentration and MeHg bioaccessiblity (r=-0442, P＜0.001). The average exposure of MeHg from marine fish was reduced by 48.3%. The contribution of Trichiurus lepturus dropped from 13% to 7%, and the contribution of Cynoglossus increased from 8% to 14%. Conclusion The MeHg bioaccessibility varied across different species of marine fish. Cooking process reduced the MeHg bioaccessibility from fish. The effects of bioaccessibility need to be considered on dietary MeHg risk assessment.