Indoleamine 2, 3-dioxygenase 1 (IDO1) is the only rate-limiting enzyme outside the liver that catalyzes the oxidation and cracking of indole rings in the tryptophan along the kynurenine pathway (KP). The overactivation of IDO1 is closely related to the pathogenesis of various human immune and neurological diseases. As an important target for the treatment of many human serious diseases including malignant tumors, the development of IDO1 inhibitors is of great practical significance. In this work, the structure and function of IDO1 both are summarized from the aspects of signal pathway, catalytic mechanism, structural biology and so on. Moreover, the current development status of IDO1 inhibitors is also systematically reviewed, which provides assistance for anti-cancer drug design based on the structure of receptors. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.