Abstract: A technique was described for determining the diffusion coefficients and distribution coefficients of contaminants passing through saturated clay samples.The technique was illustrated with reference to a number of laboratory tests involving diffusion migration of contaminants through a clayey soil of Shanghai,P.R.China.The mass of contaminant in the system was kept constant and so source leachate concentration decreased during each test.A simple theoretical model was used to analyze the test and it was shown that the diffusion coefficient and distribution coefficient from a single test could be deduced by Laplace transform method.Diffusion coefficients and distribution coefficients of Cl-,K+,Ca2+,Zn2+,Cu2+ were calculated by Laplace transform program.If was shown that the apparent diffusion coefficient of anion Cl-through the clay samples was much larger than those of cations,and the apparent diffusion coefficient of cation K+ was smaller than those of divalent cations.