Graphene/carbon nanotube (GR/CNT) composites were prepared by a modified exfoliation approach and used as capacitive deionization (CDI) electrodes. SEM and TEM images demonstrate that the CNTs are successfully inserted into the GR. Nitrogen sorption analysis and electrochemical impedance spectroscopy show that the GR/CNT composites have a larger specific surface area and higher conductivity as compared with GR, which is due to the inserted CNTs inhibiting the aggregation and increasing the conductivity in the vertical direction. Through cyclic voltammetry and galvanostatic charge/discharge evaluation, we can conclude that the prepared composites have higher specific capacitance values and better stability, suggesting that the GR/CNT composite electrodes have a higher electrosorption capacity. Power and energy density analysis shows that the GR/CNT composite electrodes have higher power density and energy density and the energy density decay is relatively slow in a wide range of power as compared with GR, which indicates that the composite electrodes exhibit low energy consumption for capacitive deionization. The desalination capacity was evaluated by a batch mode electrosorptive experiment in a NaCl aqueous solution. As compared with GR and commercial activated carbon, the GR/CNT composite electrodes exhibit excellent desalination behavior, which is attributed to the improved electric conductivity and higher accessible surface area, which are quite beneficial for the electrosorption of ions onto the electrodes. The GR/CNT composites are confirmed to be promising materials for CDI electrodes.