White muscle samples of bigeye tuna, Thunnus obesus, collected in the Atlantic Ocean and the Indian Ocean were analyzed for total (THg) and organic mercury (OHg) concentrations. A total of 231 white muscle samples showed that THg and OHg concentrations ranged from 0.217 to 0.386 (0.786 ¡Ó 0.386) and 0.143 to 2.222 (0.595 ¡Ó 0.238) mg/kg wet weight, which did not differ with other previous studies. THg and OHg were linearly correlated with fork length (cm) and body weight (kg). The THg and OHg concentrations of 121 bigeye tuna samples collected in the Atlantic Ocean were linearly correlated with fork length, body weight and age. The OHg of 110 bigeye tuna in the Indian Ocean were linearly correlated with fork length, body weight and age, but only the the THg concentrations were linearly correlated with fork length. The average THg and OHg concentrations of bigeye tuna from the Atlantic Ocean showed significantly higher value than those from the Indian Ocean (p< 0.05). Furthermore, the slope of the regression lines between mercury concentrations (THg and OHg) and fork length in the bigeye tuna from the Atlantic Ocean was significantly higher than those from the Indian Ocean (p< 0.05). It¡¦s suggested that different Hg accumulation patterns exist in the two oceans. In the Atlantic and Indian Ocean, 1.7% and 0% of the bigeye tuna, respectively, had OHg concentrations of the muscles above the authorized limit (< 2 mg/kg wet weight) set by the Department of Health, Taiwan, and 13% and 2.7%, respectively, of the levels exceeded the safety food standard (< 1 mg/kg wet weight) set by WHO and FDA. Accordingly, for adult men and women with 65 kg and 55 kg of body weight, the maximum allowable weekly intake of bigeye tuna are suggested to be 170 and 145 g, respectively.