Abstract: The sodium/iodide symporter (NIS), an integral plasma membrane glycoprotein of the basolateral membrane of the thyroid gland follicular cells, mediates the active transport of iodide into thyroid cells. In this review, the main accomplishments of the study of NIS at molecular level were concisely described, including the NIS gene, the secondary structure and electrophysiological character of NIS protein, and their regulation and tissue distribution. The impacts of NIS on thyroid disease and radioactive iodide therapy were also evaluated.