The present invention relates to 1,2,5- oxadiazole derivatives and their compositions, they are the inhibitor of indoleamine 2,3-dioxygenase, and can use what treating cancer and other illnesss, further relate to method and intermediate that such 1,2,5- oxadiazole derivatives are prepared with what. The present invention also provides the IDO inhibitor of Formulas I or its officinal salts, and wherein R1 is NH2 or CH3； R2 is Cl, Br, CF3, CH3 or CN； R3 is H or F； It is 1 or 2, etc. with n.本發明涉及1,2,5‑噁二唑衍生物和它們的組合物，它們是吲哚胺2,3‑雙加氧酶的抑制劑，且可用於治療癌症和其它病症，還涉及用於製備這樣的1,2,5‑噁二唑衍生物的方法和中間體。本發明還提供了式I的IDO抑制劑或其可藥用鹽，其中R1是NH2或CH3；R2是Cl、Br、CF3、CH3或CN；R3是H或F；和n是1或2，等等。
