The analysis of triglyceride (TG) molecular species in naturally occurring fats and oils by HPLC and LC-MS was investigated based on the partition number theory. The method using the tandem joined HPLC-UV-ELSD system with gradient elution was developed to quantify the respective TG molecular species in the fish oil. The position of DHA in the TG of a marine lipid was analyzed by the NMR method, and the procedure was established as one of the official analytical methods of the Japan Oil Chemist Society (JOCS). Additionally, the preservation of food lipids using an antioxidant like tocopherol, rosemary extract and phytic acid and its hydrolysis products for marine lipids are summarized. The Japanese traditional marine product of dried bonito, 'Katsuobushi' was examined for any lipid change during processing. The oxidized fats and oils are also reported to be a neurotoxin problem. Consequently, the control of the oxidation of fats and oils in foods is important, in order to prevent the deterioration of foods and protect human health in conjunction with the TG molecular species analysis.