The changes in the lipids of jack mackerel, Trachurus japonicus, muscle during low temperature storage were studied by using thin-layer chromatography for the separation and identification of lipids and using gas-liquid chromatography for the analysis of fatty acid composition of each lipid. First of all, the relation between total lipid and triglyceride (TG) contents in ordinary muscle of jack mackerel was elucidated. Thus, the total lipid contents varied from 2.0 % to 13.5 %. This variation was due mainly to the TG contents, while the phospholipid contents were relatively constant. The storage at 5℃ for 10 days and at -5℃ for 35 days led to the decreases in TG, phosphatidylethanolamine (PE) and phosphatidylcholine (PC) and to the smaller increases in free fatty acids (FFA). However, no accumulation of diglyceride or monoglyceride was detected and the small increase of lysolecithin was observed. Comparing the C_<16:0>, C_<18:0>, C_<20:5>, and C_<22:6> amounts decreased in TG, PE and PC with these amounts increased in FFA, it was concluded that during storage at 5℃ the most of the decreases in TG, PE and PC were caused by oxidation before their hydrolysis, whereas during storage at -5℃ these decreases were due to their hydrolysis and oxidation of PE, and some of free highly unsaturated fatty acids which were liberated by their hydrolysis were oxidized. In model system, PE was more susceptible to oxidation than TG and PC, this indicated that PE was more unstable during low temperature storage of jack mackerel muscle. During storage at -25℃ for 65 days, neither their appreciable oxidation nor hydrolysis of TG cccurred, so the increase in FFA corresponded to the decreases in PE and PC and the small increase in lysolecithin.