The proximate compositions and fatty acid profiles of Antarctic toothfish Dissostichus mawsoni that was caught in the southern Ross Sea (J, L) of the Antarctic Ocean were studied. The lipid contents of samples from J and L were 18.2 and 21.1%, respectively. The protein and ash contents were similar for samples J and L. The prominent fatty acids in the total lipids of the fish muscle were 18:1n-9, 16:1n-7, 16:0, 14:0, 18:1n-7, 20:5n-3 (eicosapentaenoic acid, EPA), and 22:6n-3 (docosahexaenoic acid, DHA). In addition, the total fatty acids of bycatch products in the toothfish stomachs (Pleuragramma antarcticum, Gerlachea australis, Pasiphaea sp., Trematomus eulepidotus, Chionodraco hamatus, Chionodraco myersi, and Neopagetopsis ionah) were determined. The prominent fatty acids in those species were 18:1n-9, 16:0, 14:0, DHA, EPA, and 18:1n-7.