Capacitive deionization (CDI) is the next generation of water desalination and softening technology by using relatively low capacitive current of electrochemical double layer. Among various carbon-based materials used for making electrode, reduced graphene oxide (rGO) has been intensively studied due to its excellent electrical conductivity and high surface area. Although Hummer method for making graphene oxide (GO) and rGO is a simple process, it remains some impurities in inherent GO and rGO which affect negatively to the CDI performance. In this work, we successfully prepared ultra purified GO and rGO by modifying Hummer method in order to remove entirely excess elements degrading the CDI performance. The electrosorption capacity of ultra purified rGO is considerably better than that of previous rGO, and maximum removal achieves 3.54 mg g(-1) at applied voltage of 2.0 V. Thus, this result could be comparable to other researches in CDI process. (C) 2015 Elsevier B.V. All rights reserved.