The lipid components, nitrogenous extracts and amino acids of dark muscle(DM) of ski-pjack (Katsuwonus pelamis) were analyzed and compared with those of white muscle (WM). WM was higher in moisture and crude protein content, and lower in crude lipid and ash content than those of DM. Contents of volatile basic nitrogen in WM and DM were 22.7mg/100g and 46.9mg/100g. Total lipid(TL) of WM and DM consisted of $79.7\%,\;71.9\%$ neutral lipid(NL), $6.8\%,\;9.5\%$ glycolipid(GL), and $13.5\%,\;18.6\%$ phospholipid(PL), respectively NL was mainly com-posed of free fatty acid, triglyceride, and PL was mainly occupied by phosphatidyl ethanolamine, phosphatidyl choline. Also Iysophosphatidyl choline and Iysophosphatidyl ethanolamine were identified in PL. In fatty acid composition of TL, NL, GL and PL, WM revealed higher contents in saturates and monoenes such as 16 : 0, 18 : 1, while DM showed higher contents in polyenes such as 22 : 6 especially. The major fatty acids of these samples were generally 16: 0, 18:0, 18:1, 20:5 and 22 : 6. Contents of total free amino acids from WM and DM were 5,982.3mg/100g and 4,450.7 mg/100g (dry base). Of free amino acids, Tau concentration was much higher in DM than in WM, Ala, Gly, Met, Arg, Thr were also high in DM. But His was much higher in concentration in W. Content of inosinic acid(IMP) in WM(680.9mg/100g) was higher than that of DM(73.1mg/100g). The degradations of IMP proceeded very rapidly in DM. DM contained much higher trimethylamine oxide and trimethylamine than those of WM. The profile of combined amino acids in these samples, were very similar, and main amino acids were Glu, Asp, Lys, Ala, Ile and Arg.