We analyzed the desalination characteristics of an MCDI (series-MCDI) stack in which carbon electrodes were connected in series and examined possible applications. The desalination performances were analyzed by measuring the potentials, currents, effluent concentrations, and pH during desalination experiments. The voltage and current changes in the series-MCDI stack were similar to the expected results of capacitors connected in series. This result means that the carbon electrodes inside the stack are performing the desalination function without a direct connection to the power supply. However, as the number of cells in the stack increased, the salt adsorption capacity (SAC) and charge efficiency decreased. From the stack voltage and internal cell potential of the stack, it was confirmed that the potential distribution inside the stack was not uniform. A higher potential was applied to the anode and cathode that were directly connected to the power supply than to the other electrodes. As a result, electrode reactions occurred, resulting in a decreased desalination performance.