Background& Aims: Most women experience the premenstrual syndrome at their reproductive ages. This syndrome is a combination of psychological, physical and behavioral changes that interfere withfamilial communication and social activities. Different methods have been suggested to reduce it; oneof them is using medical herbs. This study was carried out to evaluate the effects of curcumin on severityof symptoms of PMS.Materials and Methods: In this double-blind clinical trial, 70 students with PMS were randomlyassigned to either the curcumin or placebo groups. Each participant received two capsules daily fromseven days before menstruation to three days after menstruation for three cycles. They recorded severityof the symptoms by daily record questionnaire. The data of before interventions, and 1, 2 and 3 monthsafter interventions were analyzed by repeated measurement ANOVA and independent t-test. SPSS-18 software was used for analyses and P<0/05 was considered significant.Results: Before intervention, there were no significant differences between the mean scores of PMSsymptoms in the two groups (103.6±39.19 in curcumin group VS 106.7±44.65 in placebo group, P=0.77), but after 1, 2 and 3 months intervention, there were significant differences between the meanscores of PMS symptoms in the two groups (respectively 93.72±40/13, 91.36±49.13 and 91.45±50.49in placebo group, and 53.5±22.68, 42.1±19.1 and 29.7±11.6 in curcumin group) (P<0.0001).Conclusion: Based on results of this study, curcumin is effective in reduction of severity ofpsychological, physical and behavioral symptoms of PMS, and we suggest curcumin as treatment forPMS.