Vitamin D has been associated with the regulation of bone metabolism. However, increasing evidence demonstrates a strong association between vitamin D signaling and many biological processes to that immunostimulatory and immunomodulatory effects on the immune system. the presence of the vitamin D receptor in multiple immune cells, such as monocytes, dendritic cells, and activated T cells, vitamin D with a novel role in modulating immunological functions and its subsequent role in the development or prevention of autoimmune diseases such as systemic lupus Erythematosus, Type-1 Diabetes mellitus and multiple sclerosis. In the present review, the multiple and diverse effects of vitamin D on the immune system are reviewed.