The newly discovered Zhunsujihua porphyry Mo deposit is located in the southwestern part of the Great Hingan Range, north-east China. Molybdenum mineralization generally presents as veins or disseminations hosted in granitic intrusions, and multiple-stage hydrothermal activity has resulted in potassic, phyllic, and sericitic alteration. The mineralization process can be divided into four stages, that is, quartz-K-feldspar ± pyrite veinlets in stage I, quartz-molybdenite veinlets in stage II, quartz-polymetallic sulfide veinlets in stage III, and barren quartz-calcite veins in stage IV. Four types of fluid inclusions can be distinguished by petrography in hydrothermal quartz, including liquid-rich two-phase, vapour-rich two-phase, pure gaseous, and pure liquid inclusions, but quartz in stage I contains all types of fluid inclusions.The homogenization temperatures in quartz of stages I, II, III, and IV vary from 300°C to 520°C, 230°C to 410°C, 170°C to 260°C, and 136°C to 227°C, with salinities of 4.18-13.30 wt.% NaCl equiv., 2.07-11.10 wt.% NaCl equiv., 1.74-8.95 wt.% NaCl equiv., and 0.70-5.71 wt.% NaCl equiv., respectively. The ore-forming fluids in this deposit are characterized by high temperature and intermediate to low salinity belonging to an H 2 O-NaCl system. δ 18 O quartz values of quartz from stages I to IV range from +5.5‰ to +10.1‰, with the calculated δ 18 O fluid values ranging from -6.7‰ to +6.3‰, and the δD values of fluid inclusion waters in quartz ranging from -118‰ to -102‰. The δ 34 S values of pyrite and molybdenite from different ore stages range from 3.8‰ to 6.8‰ with an average of 5.1‰. Pyrite and molybdenite samples in the deposit have 206 Pb/ 204 Pb ratios of 18.394 to 18.766, 207 Pb/ 204 Pb ratios of 15.580 to 15.694, and 208 Pb/ 204 Pb ratios of 38.309 to 38.942. All these observations reveal that the hydrothermal fluids of the Zhunsujihua porphyry Mo deposit have a dominantly magmatic signature with an input of meteoric water during the carbonate stage, and the ore-forming components (metal and sulfur) were sourced from a greater magmatic source and some upper crustal materials.