Background: Multiple Sclerosis (MS) is the most common demyelinating disease. An autoimmune basis has been confirmed for pathogenesis of MS, and studies have shown that sex hormones such as testosterone may play a role in the disease mechanism. The purpose of this study was to survey these changes in MS patients. Materials and Methods: 31 MS patients were included in this cross-sectional study and matched with 60 healthy coses as control group. The serum testosterone level of both groups were randomly determined in follicular and luteal phases. Then the testosterone hormone levels and their correlation with the disease were studied. Results: In this study, testestrone level in patients was 0.461 ± 0.3 ng/ml in the follicular phase compared to controls with mean level of 0.82 ± 0.4 ng/ml(pv=0.011) .Mean testestrone level in female patients was 0. 58 ± 0.7 ng /ml in the luteal phase compared to controls with mean level of 0.88± 0.3 ng/ml (pv = 0.03). Patients with MS had significantly lower testosterone, in the follicular and luteal phase, but no relation with the disease was observed. Conclusion: Testestrone has a positive relation with MS. Further studies to determine the cause of relation and effect of endocrine system on MS pathogenesis and treatment are suggested.