In practice, stable Cd isotope ratios are being applied to trace pollution sources in the natural environment. However, Cd isotope fractionation during weathering processes is not yet fully understood. We investigated Cd isotope fractionation of Pb-Zn ore in leaching experiments and in the environment under natural weathering processes. Our leaching experiments demonstrated that the leachate was enriched with heavy Cd isotopes, relative to initial and residual samples (Delta(114/110) CD (leachate) (-) (initial) state = 0.40-0.50 parts per thousand, Delta(114/110) CDleachate (- residual state) = 0.36-0.53%). For natural samples, delta Cd-114/110 values of stream sediments were higher than those of the corresponding soil samples collected from the river-bank, Delta Cd-114/110(stream) (sediment - soil) can be up to 0.50 parts per thousand. This observation is consistent with our leaching experiments, which indicate significant Cd isotope fractionation during natural weathering processes. Therefore, natural contributions should be considered when using Cd isotopes to trace anthropogenic pollution in water and sediment systems.