Nutrition is known as a possible environmental factor in pathogenesis of MS. Positive clinical and biological effects of dietary supplements containing polyunsaturated fatty acids omega -3 (PUFA) in the course of autoimmune diseases such as MS have been studied. High levels of PUFA is found in fish oil which is also known as an antioxidant, anti-inflammatory and immunomodulatory agent. Several studies have evaluated the effect of fish oil as a dietary supplement in the treatment of MS however, conflicting findings are reported.