Introduction: Dysmenorrhea or painful mensturation, causing significant disruption in a woman's life each month. It is one of the most common gynecologic complaints, thought to affect approximately one half of all women. The purpose of this study was to examine whether dietary supplementation with omega-3 fatty acids of CLUPEONELLA gerrimi and engraliformis fish (Kilka) can relieve symptoms of dysmenorrhea.Methods: In this clinical trial (cross- over) study, 36 girls (aged 18-22) with dysmenorrhea were randomly allocated to two groups. In the first group 18 girls received fish oil (550 mg eicosapentanoic acid and 205 mg docosahexaenoic acid) daily for 3 months followed by a placebo for an additional 3 months. The Cox menstrual symptom scale was used to assess response to treatment. Ibuprofen 400 mg was considered as rescue dose when the symptoms were severe. Results: After 3 months of treatment with fish oil, there was a marked reduction in back pain and abdominal pain (P<0.05) Also, subjects used fish oil needed less rescue dose compare with placebo group (P<0.05).Conclusion: Our finding showed that fish oil containing omega-3 fatty acids could improve symptoms of dysmenorrhea. On the other hand, fish oil therapy can reduce the need of rescue dose to Ibuprofen 400-mg.