Abstract: Ankerite is one of the main gangue minerals at main mineralization stage of quartz-vein gold deposits in southeastern Guizhou. It plays an important role in the migration and precipitation of gold and the characteristics of fluid inclusions within ankerite can reflect the ore-forming fluid character. The authors conducted experiments on the microscopic petrography observation, homogenization temperature and freezing point of fluid inclusions, and then calculated the inclusions salinity and density. Results show CO₂ inclusions in ankerite are well developed; ore-forming fluid uniformity temperatures concentrate in 240-300 ℃ with average of 267.21 ℃, the salinity of ore-forming fluid is between 1.57%-12.96% (NaCl) with average of 15.31%(NaCl); and the mineralization density distribution ranges from 0.69 g/cm³ to 0.91 g/cm³, with average of 0.89 g/cm³. So the quartz-vein gold deposits of southeastern Guizhou are middle temperature hydrothermal deposits and the ore-forming fluid has the characteristics of high density and low salinity.