Background: Multiple sclerosis (MS) can be influenced by environmental and internal factors. One of environmental factors which may be effective on MS is different programs of physical exercise. The aim of the study was to evaluate the effect of eight weeks of selected exercise training on serum nitric oxide (NO) level and disease activity (EDSS) in women with relapsing remitting MS. Materials and methods: Subjects of the study included 27 women with relapsing remitting MS who participated in this study voluntarily and were randomly assigned to control (C), (N=12) or experimental groups (EX), (N=15). Subjects participated in progressive aerobic exercise on stationary bicycle at 60% to 80% of target heart rate, 3 day/week for 8 weeks. Serum NO concentrations were determined before and following 4th and 8th weeks of exercise training. EDSS and VO2max were assessed using Kurtzke Expanded Disability Status Scale and Bruce tests respectively, before and after exercise training. To analysis data, factorial repeated measure analysis of covariance (ANCOVA) was used at p≤0.05 significant level. Results: No significant difference was found in NO in EX group compared to C group. EDSS significantly decreased in EX group compared to C group and VO2max increased significantly after 8 weeks aerobic exercise training in EX group compared to C group. Conclusion: Physical training can be effective in improving MS through reduction of disease severity and increasing in VO2max by maintaining the balance of NO.