Bi-membranes were developed and studied as selective barrier in the transport of calcium and potassium. The bi-membranes consisted of an ion-selective membrane and a conducting polymer (polypyrrole) membrane. The ion-selective membrane acted as a selective barrier for ions while the conducting polymer acted as an electrochemically controlled barrier. The thickness of the membrane was tuned in order to obtain the best membrane transport properties. Owning to the presence of the ion-selective membrane the bi-membranes demonstrated permselectivity and selectivity towards the studied target ions. In this particular investigation NO3− was also transported with the cations across the bi-membranes. The calcium-selective membrane showed higher transport of nitrate than potassium-selective membrane. The potentiometric investigation of both membranes revealed that at high ion concentrations using this type of electrochemical system, as in bi-membranes, the co-extraction of anion together with cation into the ion-selective membrane took place. The ion couple was transported across the membrane into the receiving solution.