Membrane permeation characteristics of methanesulfonic acid and tin methanesulfonate were examined in diffusion dialysis and electrodialysis with ion-exchange membranes. In the diffusion dialysis experiments, the methanesulfonic acid permeated through an anion-exchange membrane, but did not permeated through a cation-exchange membrane. The apparent diffusivities of methanesulfonic acid through the anion-exchange membrane were determined with the flux of methanesulfonic acid and the concentration difference between the compartments. The values were the same order of hydrochloric acid permeation in the anion-exchange membrane. In the experiment of electrodialysis for tin methanesulfonate solution, methanesulfonic acid moved to the anode-side strip compartment through the anionexchange membrane, but tin ion moved to the cathode-side strip compartment through the cation-exchange membrane. These fluxes were almost proportional to the current density, and the flux of tin ion agreed with the theoretical value corresponding to that di-charged ion permeates at the transport number equal to unity.