The selective separation of Ni(2+)/Co(2+) ions from their dilute solution using continuous electrodeionization process, facilitated with complexing agent, was investigated in this study In order to Increase the selective removal of Ni(2+) ion. EDTA was used as a complexing agent and Taguchi method was implemented for systematic design of the experiments The statistical analysis of the experimental results showed that EDTA Ni mole ratio and feed flow rate were the most influential parameters on performance of the process with contributions of 55 3% and 28 1%, respectively The comparative experiments proved that the effective separation of Ni(2+)/Co(2+) in the absence of EDTA was impossible Also, electrodeionization process was more effective than electrocatalysis process for selective separation of Ni(2+)/Co(2+) when EDTA was used in both methods. Ni(2+)/Co(2+) ions molar ratio increased from its initial value of 3 to a final value of 154.6 at optimum operating condition, as predicted by Taguchi method. Finally, obtained results showed that the applied procedure can be considered as a promising method for selective separation of Ni(2+)/Co(2+) ions from their dilute aqueous solution. (C) 2010 Elsevier B.V. All rights reserved