Background: Primary dysmenorrhea is a prevalent disorder and its unfavorable effects deteriorates the quality of life in many people across the world. Based on some evidence on the characteristics of fenugreek as a medical plant with anti-inflammatory and analgesic properties, this double-blind, randomized, placebo controlled trial was conducted. The main purpose of the study was to evaluate the effects of fenugreek seeds on the severity of primary dysmenorrhea among students. Methods: Unmarried Students were randomly assigned to two groups who received fenugreek (n=51) or placebo (n=50). For the first 3 days of menstruation, 23 capsules containing fenugreek seed powder (900 mg) were given to the subjects three times daily for two consecutive menstrual cycles. Pain severity was evaluated using a visual analog scale and systemic symptoms were assessed using a multidimensional verbal scale. Results: Pain severity at baseline did not differ significantly between the two groups. Pain severity was significantly reduced in both groups after the intervention; however, the fenugreek group experienced significantly larger pain reduction (p < 0.001). With respect to the duration of pain, there was no meaningful difference between the two cycles in the placebo group (p=0.07) but in the fenugreek group, the duration of pain decreased between the two cycles (p < 0.001). Systemic symptoms of dysmenorrhea (fatigue, headache, nausea, vomiting, lack of energy, syncope) decreased in the fenugreek seed group (p < 0.05). No side effects were reported in the fenugreek group. Conclusion: These data suggest that prescription of fenugreek seed powder during menstruation can reduce the severity of dysmenorrhea.