The 'lsquoin-diffusionrsquo method was used to study the diffusion behavior of Eu(III) in compacted bentonite. The results (K d, apparent and effective diffusion coefficients) derived from the capillary method are in good agreement with the literature data for similar bentonite dry densities and similar radionuclide concentrations, and fits the Fick's second law very well. The method was used to study the effect of solution concentration (10-7-10-3 mol/l) on the diffusion and sorption behavior in compacted bentonite. The experiments were carried out in synthetic groundwater, at room temperature. The results suggested that the diffusion of Eu(III) in the bentonite was independent on the density of bentonite, but dependent on the solution concentration. In agreement to the literature, the K d values from the capillary experiments are in most cases lower than those from batch experiments, they are about one-half to one-third the value to those from batch experiments. The difference between the K dvalues from capillary and batch experiments are a strong function of the bulk density of the bentonite. The results suggest that the content of interlaminary space plays a very important role to the transport of Eu(III) in compacted bentonite.