The Lanping basin is an important Pb-Zn-Cu-Ag polymetallic province in southwestern (SW) China. Mineralization types in the basin include mainly MVT Pb-Zn deposits, vein-type Cu deposits, and minor quartz vein-type Pb-Zn deposits. In this study, we analyzed the total Hg (THg) content and Hg-S isotopic compositions of sulfides from two types of Pb-Zn deposits in the basin, and investigate the Hg isotope fractionation mechanism and its major controlling factors in the Pb-Zn ore-forming process. At the Shangnuluo quartz vein-type Pb-Zn-Sb deposit, sulfides (especially sphalerite) show a wide delta Hg-202 range (-0.40 to 2.71 parts per thousand), suggesting that Hg-0 evaporation from hydrothermal fluids occurred during the ore formation. Negative THg vs. delta Hg-202 correlation in the sphalerites suggests a mixing of Hg from the vapor phase (low delta Hg-202, high THg) and the residual aqueous phase (high delta Hg-202, low THg). The negative Delta Hg-199 (-0.42 to -0.08 parts per thousand) suggests that the Hg was sourced from the metamorphic basement, whereas the negative delta S-3(4) values (-13.0 to - 2.7 parts per thousand) suggests that the sulfur was mainly sourced from sedimentary sequences, possibly related to the organic matter decomposition and thermochemical sulfate reduction (TSR). For the Liziping and Fulongchang MVT Pb-Zn deposits, sulfides have relatively narrow delta Hg-202 range (-1.46 to 0.25 parts per thousand), suggesting limited H-g evaporation during the mineralization. Lower delta Hg-202 values were observed in the early-stage sulfides from these two deposits, probably due to the preferential precipitation of lighter Hg isotopes in these early-stage sulfides. Sulfides from both deposits have negative Delta Hg-199 values (-0.24 to 0.01 parts per thousand), suggesting that the Hg was also derived from the metamorphic basement. Sulfide delta S-3(4) values from the two deposits are positive, which also suggests that the sulfur was sourced from sedimentary sequences, but mainly related to TSR under relatively low-temperatures. Sulfides from different Pb-Zn deposit types in the Sanjiang Tethyans Metallogenic Belt fall into distinct fields in the delta S-3(4) vs. delta Hg-202 (or Delta Hg-199) diagrams, indicating that the integration of S and Hg isotopes is useful to discriminate different types of Pb-Zn deposits.