Contamination of methylmercury (MeHg) in aquatic products has been a wide spread health concern. The objective of this study is to determine total mercury (THg) and MeHg concentrations in different species of aquatic products from major offshore farms in China, and to assess health impacts from consumption. Results showed that the concentrations of THg and MeHg ranged 5.6–328.4 ng/g (wet weight) and 4.3–303.6 ng/g (wet weight) in aquatic products, respectively, and were very variable among species and origin sources. Target hazard quotient (THQ) suggested that MeHg exposure via consumption posed high health risks to children aged 2–7 and higher income families. Residents above the age of 13 and with low income have relatively lower health risk of MeHg exposure. Health impacts on heart attacks and newborns’ IQ from MeHg exposure were evaluated using dose-response relationships. Results showed that mother’s consumption of aquatic products (at 6 ounce per day) may cause a loss of 0.38 IQ points for newborns. For non-pregnant, consumption of aquatic products may cause an increase rate of mortality and morbidity of heart attacks at 10.59 and 78.45 per 100,000 persons, respectively. The negative health impact of consuming seawater fish was higher than freshwater fish.