A useful formulation of ion-adsorption kinetics is introduced based on our recent researches. The chemical reaction kinetics and diffusion kinetics are simultaneously analyzed combining with the Einstein’s viscosity formula. The rate-determining steps are quantitatively determined by estimating the relative magnitude of the kinetics resistances in the boundary film and the particle. The key concept of this method is an addition theorem of film-diffusion kinetic resistance and the particle-diffusion kinetic resistance. While in hydrophilic polymers, the thickness of boundary film decreases due to the attractive force between the ion and the surface, in hydrophobic polymers, it increases with the amount of hydrophobic components. This is confirmed by using chitosan resins with hydrophilic/hydrophobic components. The experiments are based on the batch method, and degree of film-diffusion control and particle-diffusion control is determined simultaneously. The film mass-transfer coefficient in the boundary film is also determined from a simple plotting of the experimental data. This method is also applicable to ion-exchange kinetics by summing the kinetic resistances at each step in the ion-exchange reaction and the mutual diffusion. Our method will serve as a guiding tool for designing of adsorption agents and ion-exchangers. Copyright © VBRI Press.