Major ions and Sr2+ concentrations and Sr isotopic compositions of two major river systems were measured in Guizhou karst region. The chemical composition of these rivers in the karst region represents that of river water from the typical carbonate areas. Its hydrogeochemical characteristics are different from those of global major rivers: The river and its tributaries have high total dissolved solid concentrations, with Ca²⁺ and HCO^-3 being dominant, Ma²⁺ and SO^2-₄ coming next. Both Na⁺+K⁺ and Cl^-+Si account for 5%~10% of the cations and anions, respectively. These rivers have high total concentration (TZ⁺) ranging from 2.0 to 5.5 meq/L, which are significantly higher than those of the global river averge (TZ⁺=0.725meq/L). The chemical and isotopic compositions of these rivers are largely under controll by the geological signatures of their drainage areas. The Wujiang River system draining carbonate strata show high Sr²⁺ concentrations(1.07~9.70) and lower ⁸⁷Sr/⁸⁶Sr ratios of 0.7077~0.7110, as compared with the Yuanjiang River system (⁸⁷Sr/⁸⁶Sr=0.7090~0.7145, Sr²⁺=0.39~1.32) draining detrital strata. The end-member identification by the intercorrelations between chemical and isotopic ratios shows three main sources, which are derived from weathering of limestone, dolomite and silicates. The Wujiang River system has characterized by low Na/Ca, Mg/Ca mole ratios (0.05~0.34 and 0.18~0.79, respectively), showing a strong influence of limestone, about 96% of solutes derived from the weathering of carbonate. On the other hand, the Yuanjiang river system show high Na/Ca mole ratio from 0.06~1.80, Mg/Ca from 0.23~1.30, suggestive of a strong influence of limestone and dolomite weathering, about 90% of solutes derived from the weathering of dolomite in the Wuyanghe river system and about 54% of solutes derived from the weathering of limestone in the Qingshuijiang river system.