© 2020 Society of Pharmaceutical Sciences of Ankara (FABAD). All rights reserved.selenium is a trace element that has important functions within the body. it is suggested that there is a link between selenium levels and thyroid functions since the enzymes involved in the synthesis of thyroid hormones are selenoenzymes. selenium is also required for the normal functioning of antioxidant defense mechanisms and the reduction of oxidative stress caused by Hashimoto's thyroiditis. Although studies on selenium supplementation in autoimmune thyroid diseases are limited, the data suggest that selenium treatment may have beneficial effects. in this review the roles of selenium, an important trace element which is essential for many vital functions particularly on the oxidant/ antioxidant balance, on vital functions in the organism, effects on thyroid functions and its use as an alternative treatment or supplement in Hashimoto's thyroiditis will be emphasized.