Sorption and diffusion are important processes in the transport of radionuclides through mixtures of bentonite and crushed granite. Sorption was investigated by batch tests? and the diffusion of I-125 and Sr-90 in compacted mixtures was investigated using through-diffusion tests. The distribution coefficients of Sr-90 onto the mixtures of bentonite and crushed granite depended largely on the proportion of bentonite. The distribution coefficient of Sr-90 on the bentonite decreased with decreasing the solution-to-bentonite ratio. It was found in desorption tests that Sr-90 was sorbed via an ion exchange reaction. When the dry density for the mixture of 30% bentonite and 70% crushed granite was 1.4 Mg/m(3), the apparent diffusion coefficients of I-125 and Sr-90 were 1.4 X 10(-10) and 6.7 x 10(-12) m(2)/sec, respectively. The corresponding diffusion coefficients for the dry density of 2.0 Mg/m(3) were 7.9 X 10(-11) and 3.4 X 10(-12) m(2)/sec for I-125 and Sr-90, respectively. At the high dry density, the contributions of surface diffusion and pore diffusion to Sr-90 diffusion were comparable in magnitude. At this higher dry density, the diffusion of I-125 through the pores was reduced by the mechanism of ion exclusion. The diffusion of radionuclides in the bentonite/crushed granite mixture was dominated by the bentonite. This could be explained by the concept of effective clay dry density. When the effective clay dry density of a mixture was equal to the dry density of pure bentonite? then the diffusion coefficient for the mixture was close to that for pure bentonite.