Abstract: In order to know the characteristics of water-rock interaction and the sources of the contaminants in the ground water system of the karstic area,we carry out a study on the water geochemistry of the surface and ground water in Guiyang,the capital city of Guizhou Province,China.The waters are characterized mainly by the HCO₃ and SO₄ type,as well as their mixed type.The solutes of the studied waters are mainly derived from the weathering of the carbonate and clastic sedimentary rocks,among which the sulfate ions are probably from the dissolved gypsum and the oxidation of the sulfide minerals in coal- containing strata.Most of K⁺,Na⁺,Cl^-,SO₄^2-,and NO₃^- are anthropogenic in origin.The results of this work are applicable to the assessment of water quality and human impacts on the ground water system,and can be used as the data-base for the protection and exploitation of water resources from the surface/ground water system in the karstic area.