『Abstract
　The aim of this paper was to evaluate the chemical weathering rate at Alto Sorocaba basin, Sao（aの頭に〜） Paulo state, Brazil, as it an important parameter on geomorphological characterization of continents. Several tools may be used for such evaluation, and this work compares the results obtained from analytical data involving the uranium concentration, the ²³⁴U/²³⁸U activity patio and the major cation concentration for samples of waters, soils, and rocks from that basin. The use of the natural uranium as a tracer in weathering rate rocks studies is advantageous since this element is virtually absent in rainwater and also allows obtaining the dissolution rocks coefficient by the ²³⁴U/²³⁸U activity ratio. The Alto Sorocaba basin has serious environmental problems in terms of the quality of the rainwater and river waters, and, consequently, the geochemical balance using the main cations presented some difficulties. However, measuring of the weathering rate utilizing the U-isotopes method corresponded to 14μm/year that allows estimating a time of 72,000 years to weather 1 m of rock at Sorocaba River upstream from Itupararanga Reservoir, under the present climatic conditions.

Keywords: Weathering rate; Hydrogrphic basin; Uranium isotopes』

Introduction
General features of the studied area
Sampling and analytical methods
Discussion
　Chemical analyses of rocks and soils
　Hydrochemical data for rainwater
　Hydrochemical data for river waters
　Equations adopted for estimating weathering rates
　Weathering rates in the basin
Conclusion
Acknowledgments
References