The self-diffusion of RE isotopes in porous cation exchangers with various particle size and in several MR-type resins in EDTA solutions of rare earths was studied. The intraparticie effective diffusivities De of Ce, Tb and Yb were measured by isotopic ion exchange, De was affected by the concentration of the bulk solution and was separated into a solid phase diffusivity Dg and a macropore diffusivity Dp using Kataoka’ s didisperse pore model. It shows that the model can be applied to express the kinetic process; De much larger than De and Dg is nearly equal to De. Solid phase resistance is a major component of resistance to the exchange for porous resins.