Background: Autoimmune mechanisms are involved in the etiology of Alopecia areata. It is also shown that Selenium has some effects on regulation of autoimmune mechanisms. Objective: To compare the plasma level of Selenium between those with and without Alopecia areata. Patients and Methods: In this case-control study, 29 patients with Alopecia areata referred to Razi hospital in Tehran, and 29 persons without this disease were selected consequently. Plasma level of Selenium was determined and compared between the groups. Results: The mean age of cases was 24.9±10.5 and of controls was 29.1±10.5 years. In both groups 15 (51.7%) patients were male and 14 (48.3%) of them were female. The mean plasma Selenium level in cases was significantly lower than what was observed in controls (62.1±13.3 g/l vs. 88.3±13.2 g/l, P<0.0005). Conclusion: This study indicated that mean plasma Selenium level in patients with Alopecia areata was lower than those without this disorder. It is recommended to evaluate the effects of adding Selenium to dietary regimen of patients with Alopecia areata.