The ion exchange kinetics of DL-lysine monohydrochloride on Amberlite IRA-420 have been studied. Ionic diffusivity of hydroxyl anion, which is supposed to be equal to the interdiffusion coefficient, has been evaluated by fitting experimental kinetic data to a theoretical model based on the continuity equation of the CI" anion in solution filling the pores of the resin. Because of changes of both viscosity with ionic concentration and co-ion behavior in solution at high concentrations, a variation of ionic diffusivity of hydroxyl anion has been observed. In order to predict the dynamic behavior of fixed beds a simple mathematical model including both equilibrium isotherm and ionic diffusivity of hydroxyl anion has been developed. Likewise, resin regeneration using NaOH solutions has been investigated. The results show the feasibility of the procedure of purification and regeneration and they have been used to design a plant for the treatment of 50 Tm/yr of DL-lysine monohydrochloride.