The separation performance of Na+ ions from NaCl solution has been investigated by electrodialysis at constant voltage mode of operation. TS-1-10 electrodialysis equipment (Tokuyama) modified with rotameters was employed in experimental studies. During an unsteady-state run of the ED system, both inlet and outlet concentrations of both concentrate and dilute streams were measured at time intervals of 5 min until the current drops to less than 0.01 A. The effects of parameters such as electrical potential, applied (DC) and flow rate of streams on the performance of separation were observed. The efficiencies of each run were evaluated as specific power consumption with the electrical energy consumed only in stack, Current efficiency was represented as a function of flow rate, which is based upon the mass transfer coefficient. The model proposed was in very good agreement at all flow rates at low potential applied, however, at the highest flow rate at other potentials, small deviations were found.