Transport phenomena of aniline through Na+-, K+-, and Cs+-form of a perfluorosulfonate ion-exchange membrane, Nafion(R) 117, under a flow of dc current, electrotransportation, were investigated. In each form, an increase in transport number of aniliniumcation was observed in the current density range from 0.3 to 1.3 mA cm-2. The transport number of the anilinium cation in Cs+-form was larger than that expected from the concentration and diffusion coefficient of the anilinium cation in Cs+-form Nafion. These aniline transport phenomena may be attributable to a structural change of Nafion or a decrease in hydrophobic interaction between the anilinium cation and Nafion caused by the flow of de current.