Electrodialysis (ED) was used to purify ionic liquids systems. It was expected that impurity ions could be separated from the ionic liquid system. Competitive transport behavior was extensively investigated between ionic liquids and impurity ions. [BMIM][CH3COO] and NaCl were used as a model ionic liquid and impurity ions, respectively. Two types of membranes including homogeneous and heterogenous phase membranes were used. Under a flow rate of 375 ml/min and temperature of 25 degrees C, ED was operated at different voltages and initial feed concentration to evaluate the competitive transport. Experimental results showed that Na+ and Cl migrated much more rapidly than [BMIM](+) and [CH3COO](-), respectively. It was found that the much better purification results could be obtained by using homogeneous phase membranes. Appropriate operating conditions were selected: voltage of 4 V and initial feed concentration of 100 mmol/l.