The δ~(18)O and δD values for meteoric water samples collected from eastern Xizang andwestern Sichuan and Guizhou show a linear correlation and can be described by the followingequation:δD=8.22δ~(18)O+18.99.The isotopic compositions of these meteoric waters alsoexhibit obvious altitude effect.There have been found negative correlations between δ~(18)O,δDand the elevation,which are characterized by—δ~(18)O‰=0.0031H(m)+6.19 and—δD‰=0.026H(m)+30.20.The average δ~(18)O and δD values for meteoric waters in the areaswith an altitude of more than 4,000m above sea level are equal to—18.70 and—137.8‰,respectively.It is evident that the δ~(18)O and δD values for plateau lake waters depend ontheir water supply.The δ~(18)O and δD values for the water in lakes where the evaporationrate is greater than the recharge rate,are approximately three or four times higher than thoseof supply water,averaging—5.74 and—60.5‰,respectively.The oxygen and hydrogenisotopic compositions of geothermal waters as compared with those of local meteoric waters inadjacent areas show that the latter seems to be the main water-supply source. The δ ~ (18) O and δD values ​​for meteoric water samples collected from eastern Xizang and western Sichuan and Guizhou show a linear correlation and can be described by the followingequation: δD = 8.22δ ~ (18) O + 18.99. The isotopic compositions of these meteoric waters also exhibit the negative correlation between δ ~ (18) O, δDand the elevation, which are characterized by -δ ~ (18) O ‰ = 0.0031H (m) +6.19 and-δD ‰ = 0.026H (m) + 30.20. The average δ ~ (18) O and δD values ​​for meteoric waters in the areas with an altitude of more than 4,000 m above sea level are equal to -18.70 and -137.8 ‰, respectively.It is (18) O and δD values ​​for the water in lakes where the evaporation rate is greater than the recharge rate, are approximately three or four times higher than those of supply water, averaging-5.74 and -60.5 ‰, respectively. The oxygen and hydrogenisotopic composi tions of geothermal waters as compared with those of local meteoric waters inadjacent areas show that the latter seems to be the main water-supply source.