Objective: To modify yeild of milk fat and to improve fatty acids profile of milk fat with supplementation of the diet with fish oil enrich in omega-3 fatty acids, especially, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Design: Clinical trial. Animals: Ten dairy cows (treatment group, n=5 and control group, n=5). Procedure: Different amounts of fish oil were fed to the treatment group for one or two weeks: 100ml/cow/day for two weeks, 300 and 500mVcow/day each for one week. Statistical analysis: Data were compared between groups using unpaired t-test at p< 0.05. Results: Feeding fish oil depressed milk fat percent. The concentrations of milk protein and dry matter, however, remaind unchanged. The concentrations of unsaturated fatty acids increased but those of saturated fatty acids decreased. Clinical implications: Supplementation of cow's diet with fish oil may modify milk fat yeild and may improve the quality of milk fatty acids. This may increase per capita consumption of milk and its products.