Selenium is an essential trace element in human body and it exhibits critical functions of antioxidant and improvement immunity in human body. In recent years, more and more studies have revealed other effects of selenium such as antagonistic toxins, regulation of signal transduction and epigenetic modifications, and these novel researches provide new ideas for further exploration of the etiology, pathogenesis, and prevention and treatment of environmental-related diseases. In this paper, we reviewed the research progresses of selenium in biological effects, epigenetic modifications and its relationship with environmental associated diseases to further explore the biological potential and health effects of selenium for benefiting humankind better.