Abstract: Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) catalyze the initial and rate limiting step in the catabolism of tryptophan, which is related to tumor immune tolerance and poor prognosis in patients. In this regard, two enzymes have become important therapeutic targets for tumor immunotherapy. So far, nine IDO1 inhibitors and three IDO1/TDO dual inhibitors have entered clinical trials. This review summarizes the research progress of IDO1 inhibitors, TDO inhibitors and IDO1/TDO dual inhibitors from the perspective of medicinal chemistry.