To study total mercury concentration ([Hg]) in organ tissues and feathers, 13 carcasses of adult Black-tailed Gull Larus crassirostris were collected at the breeding colony on Kabushima (Kabu Island), western Pacific Ocean, at the northernmost point of Japan’s Sanriku Coast. [Hg] in liver (10.7±6.5 μg/g dry weight±S.D. and 3.2±2.1 μg/g wet weight±S.D.), kidney (6.7±4.8 and 1.8±1.3), breast muscle (3.3±2.3 and 1.0±0.3), heart (4.5±3.0 and 1.1±0.7) and brain (2.8±2.3 and 0.7±0.6) were 2.6-12.5 times higher than in previous studies of the same species. The order of [Hg] concentrations in Black-tailed Gull feather tracts was: inner primaries (P1-P5, 11.2±4.9 μg/g dry weight±S.D)>breast feathers (6.5±2.0)>secondaries (S1-S15, 2.8±1.9)>outer primaries (P6-P10, 2.5±1.9)>rectrices (R1-R6, 1.6±1.4).