Fatty acid of six pelagic fish ( Decapterus maruadsi , Sardinella aurita, Decap terus lajang , Pneumatophorus japoni cus, Trachurus japonicus, Rastrelliger kanagurta ) were studied. Saturated, Monounsaturated, Polyunsaturated fatty acids represent 35. 24%- 38. 60% , 23. 59%- 30. 07% , 33. 06%- 40. 33% of the total fatty acids in fish oil respectively, EPA and DHA represent 2. 35% - 3. 62% and 17. 95%- 24. 49%, .- 3FA/ .- 6FA > 2. The major fatty acids of SFA, MUFA, PUFA are respectively C16B0、C18B0; C18B1; DHA、C20B4、EPA and C22B5. When the lipid content increased the PUFA% decreased, which might be related to reproductive activities. The compositional percentage and content of some fatty acids show larger f luctuations in one year. Adopt ing the mult iple regression, the compositional percentage and content variations of some fatty acids are found to depend on most clearly on the lipid content , and on the season, but no more relations with body length.