The diffusivity of clavulanic acid in different porous systems (Amberlite IRA400, activated carbon and two ion-pair adsorption systems based on Amberlite XAD4 and activated carbon as matrixes and water-soluble quaternary ammonium salts as ion pairing substances) was investigated by batch adsorption experiments. The experimental data were described by using a model based on diffusion with instantaneous adsorption and/or reaction in a homogeneous sphere and the effective diffusion coefficients were calculated under different operation conditions. The influence of sorbate concentration, temperature and competitive components on the diffusivities was discussed from the viewpoint of the ruling mechanisms. A comparison between the kinetic characteristics of the investigated systems showed that the ion-pair system XAD4-ABDA is the most advantageous for the adsorption of CA.