The chemical composition variations of the Indian mackerel (Rastrelliger kanagurta) from Karachi coast were investigated seasonally over the period of one year (2004-2005). Moisture, crude protein, fat and ash contents varied from 70.11-74.41%, 16.02- 20.09%, 3.0-12%, and 0.89-1.35% respectively. The seasonal data indicated that the main fatty acids of the total lipid were C16:0, C16:1, C18:0, C18:1, C20:5 and C22:6. Total contents of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) percentages varied from 31.6-46.85%, 20.5-27.9%, and 26.8-40.85% respectively. Eicosapentaenoic acid (EPA, C20: 5n-3) and docosahexaenoic acid (DHA, C22: 6n-3) of omega 3 series which have specific importance in nutritional values concept, were the major fatty acids. The lowest EPA and DHA were found to be in July and highest in November to March.