Abstarct: Background & aim: Primary dysmenorrhea or painful menstruation, in the absence of any specific pelvic diseases, is one of the most common complaints in women’s medicine. The aim of this study was to investigate the effect of 8 weeks of Aerobic exercise and intake of Magnesium supplementation on primary dysmenorrhea in pupil girls. Methods: This quoi- experimental trial study was on students' dormitories 15-18 years old with primary dysmenorrhea in Bakharz city. Pupil girls were randomly divided into 4 group ؛1- Aerobic exercise (n=15)\-2 Magnesium supplement (n=12)\ 3-exercise plus aerobic exercise groups (n=15)\ 4-control (n=10). Aerobic exercises were carried out under the supervision of a fitness instructor for eight weeks. The Magnesium supplement groups used 250 miligaram Mg daily during two subsequent menstruation cycles. The exercise with Magnesium supplement groups participated in 8 weeks of Aerobic training (3 times a week) besides intake of Magnesium supplementation. The control group had no intervention. Data were collected included demographic questionnaire\ visual pain scale (VAS)\ inventory validation of menstrual disorders (MDQ) Before and after eight weeks\ participants completed the menstrual disorders, questionnaire and severity of pain was evaluated by visual analogue scale (VAS). Data were analyzed using SPSS21 software. Normal distribution of the data were assessed using K-S normality test and data were analyzed using Anova one way at significance level of P>0.05. Results: The result of this study showed significant improve of pain and average psychological and physical symptoms after 8 weeks intervention in three group (aerobic exercise\ Magnesium supplement , exercise plus Magnesium supplement groups). Average score MDQ and the average score VAS in all groups except the control group was reduced (P>0.05). Conclusion: Aerobic exercise and intake of Magnesium supplementation can reduce severity of primary dysmenorrhea. So this method regarding its cost-effectiveness can be used in primary dysmenorrhea.