Vitamin B_<12> contents in skipjack tuna meats and internal organs were assayed by the microbiological method authorized in the standard tables of food composition in Japan (5th Revised and Enlarged Edition). The dark meat (chiai), heart, and liver contained substantial amounts (〜63.9μg/100g) of vitamin B_<12> relative to the other meats and organs. More than half (55.8%) of total vitamin B_<12> contents detected in the tested tissues were recovered in the dark meat. The results indicate that the skipjack dark meat is an excellent vitamin B_<12> source.