Adsorption of Sr2+ onto kaolinite has been studied by means of a radiotracer technique using the Sr-90 isotope. Bangham's and McKay models have been applied to kinetic results in Sr2+ concentrations between trace -0.1 mol.L-1. The magnitudes of film and intra-particle diffusion coefficients are 10-10 and 10-14 m(2)center dot s(-1), respectively. Concentration dependence of diffusion coefficients indicated that Sr2+ ions are adsorbed on two different adsorption sites by an exothermic and spontaneous process. The Freundlich isotherm parameters and exchange equilibrium constants derived from selectivity coefficients indicate that Sr adsorption are depressed by competing cations in the order of Na+< Mg2+< Al3+.