A model of ionic surfactant-selective electrodes with mobile ionic sites is proposed. The steady-state concentrations of the active species are calculated. The electrochemical impedance of the membrane immersed between electrolytic solutions is given. This model is in good agreement with the experimental results obtained on PVC membranes with various amounts of plasticizer sensitive to various ionic surfactants, The conclusion shows that to obtain a good sensitive membrane the dissociation of the species in the membrane is quite important and ionic transfer has to be fast.