The Changtuxili Ag- Pb- Zn- Mn deposit, which is located in the Dongwuqi area of Xilin Gol League, Inner Mongolia, is a newly discovered polymetallic deposit in the Xilinhaote- Huolinguole Pb- Zn- Ag- Cu- Mo polymetallic metallogenic subzone of the middle and southern Da Hinggan Mountains polymetallic metallogenic belt. The discovery of the deposit fills the prospecting gap in the area. Ore- hosting strata contain one suite of intermediate- felsic volcanic lava intercalated with volcaniclastic rocks of the Baiyingaolao Group, with orebodies occurring as veins and lenticular by faults. The junction areas of NW and NE trending structures are favorable for mineralization. Hydrothermal mineralization can be divided into four stages: quartz- pyrite stage, lead zinc metal sulfide stage, silver mineral stage and quartz carbonate stage. Based on a detailed analysis of geological characteristics, this study carried out S, Pb, C and O isotopic analysis to understand the origin of ore- forming materials and genesis of the Changtuxili deposit. The δ 34 S values of polymetallic ore range from 0. 6‰~4‰ and display characteristic of tower- shaped distribution, indicating that the sulfur derived from relatively single magma source. The 206 Pb/ 204 Pb ratios of sulfide ores range from 18. 129 to 18. 177 (18. 155 on average), 207 Pb/ 204 Pb from 15. 500 to 15. 561 (15. 533 on average), and 208 Pb/ 204 Pb 37. 849 to 38. 049 (37. 959 on average), indicating that lead isotope ratios are relatively stable. The μ values vary from 9. 3 to 9. 41, while ω values vary from 34. 69 to 35. 82. The Pb isotopic compositions and all analytical data indicate that the lead was mainly derived from the mixture of crust- mantle materials. The sulfur and lead isotopic compositions of the Changtuxili deposit show high similarity with that of the polymetallic deposits in the Da Hinggan Mountains, indicating that they may have similar source of metallogenic material. δ 13 CV- PDB values of -6.1~-7.9‰ and δ 18 OV- SMOW values of +8.7‰~+13.2‰ indicate that the carbon isotope mainly derived from the deep source magma and was affected by the low temperature alteration in late metallogenic stage. The formation of siderite may resulted from decreasing of temperature and the coupling reaction of water/rock reaction. It can be speculated based on the age of country rocks that the deposit formed at about 130~140Ma, consistent to the peak period of mineralization in the middle and southern sections of the Da Hinggan Mountains Range. The Changtuxili deposit was the product of the gradual evolution of the deep magmatic fluid, which provided thermal and metallogenic materials for the formation of deposits. It is preliminarily believed that the genetic type of the Changtuxili Ag- Pb- Zn- Mn polymetallic deposit belongs to epithermal polymetallic deposit.