To elucidate the difference of the taste between lean muscle Akami and fatty muscle Toro of bigeye tuna Thunnus obesus, chemical components, such as proximate, fat, fatty acid, and extractive components were compared. The effects of tuna oil addition on the taste of 80% ethanol extracts were also investigated by sensory evaluation. Fat content was lower in Akami (0.5%) than in Toro (6.6-7.2%). Large amounts of anserine and histidine were detected in all muscles, but anserine content was higher in Akami and histidine content was higher in Toro. By sensory evaluation, no difference was observed in whole taste intensity and the taste profile between Akami and Toro extracts. Addition of tuna oil to the extracts as emulsion, however, decreased sourness significantly and tended to increase sweetness and decrease bitterness. The pattern similarity analyses revealed sweetness was the factor which was most contributable to the change of the taste.