Oxidative stress maybe involved in the patho-etiology of menstrual-associated complications. Curcuminoids, are polyphenolic natural compounds that have potentially important functional activities. This triple-blind, randomized, placebo-controlled trial was performed to investigate the effects of a curcuminoids on oxidative stress and antioxidant capacity in girls with premenstrual syndrome (PMS) and dysmenorrhea.Eighty young girls with both PMS and dysmenorrhea were randomly given either curcuminoids (500 mg+5 mg piperine) or a placebo daily, for a period from 7 days pre- until 3 days post- initiation of menstrual bleeding for 3 successive menstrual cycles. The total antioxidant capacity and free radical scavenging activity of serum and urine were quantified via ferric reducing/antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) methods, respectively. There were no significant differences between the placebo and curcumin groups, with respect to the age, dietary intake and biochemical/anthropometric indices (p＞0.05). The curcumin treatment significantly increased the free-radical scavenging activity of serum compared to the treatment with placebo (p=0.031). Although, no significant changes were found in serum and urinary levels of FRAP, DPPH and MDA between the groups (p＞0.05). Curcumin treatment did increase free-radical scavenging activity and antioxidant potential in girls with PMS and dysmenorrhea. Investigations with higher doses and duration of curcumin are required to verify our findings.