Thermal karst groundwaters with temperatures ranging from 32.8 to 62.5 ℃ were found at Taiyuan(太原) City,the capital of Shanxi(山西) Province.To identify the origin of the thermal groundwater,the following tracers were used in this study:δD,δ18O,4He,3He/4He,and major chemical constituents in water.Hydrochemical and isotopic data indicate that the thermal groundwaters in the basin area are a mixture of thermal waters from the West Mountain and those from the East Mountain.Furthermore,the 4He and 4Heexc concentrations of the thermal groundwater samples are usually lower than those of the cold groundwater samples,and there is an evidently negative correlation between the temperature and the 4He concentration in thermal groundwaters from the West Mountain and the ba-sin,which means that with the increase in temperature,the He concentration increases in the vapor phase and decreases in the aqueous phase.In the plot of 3He/4He vs.4He/20Ne of all water samples:air,crust,and mantle,all thermal groundwater samples are distributed near the line between the point of air and that of crust,suggesting that atmospheric and crustal helium is the main source for that in thermal groundwaters.In other words,there are no mantle-derived fluids mixed in the thermal groundwaters. Thermal karst groundwaters with temperatures ranging from 32.8 to 62.5 ° C were found at Taiyuan City, the capital of Shanxi Province. To identify the origin of the thermal groundwater, the following tracers were used in this study: δD, δ18O , 4He, 3He / 4He, and major chemical constituents in water. Hydrochemical and isotopic data indicate that the thermal groundwaters in the basin area are a mixture of thermal waters from the West Mountain and those from the East Mountain. Futurerther, the 4He and 4Heexc concentrations of the thermal groundwater samples are usually lower than those of the cold groundwater samples, and there is an evidently negative correlation between the temperature and the 4He concentration in thermal groundwaters from the West Mountain and the ba-sin, which means that with the increase in temperature, the He concentration increases in the vapor phase and decreases in the aqueous phase. The plot of 3He / 4He vs. 4 He / 20 Ne of all water samples: air, crust, and mantle, al l thermal groundwater samples are distributed near the line between the point of air and that of crust, suggesting that atmospheric and crustal helium is the main source for that in thermal groundwaters.In other words, there are no mantle-derived fluids mixed in the thermal groundwaters.