Capacitive deionization (CDI) process is an emerging process for water desalination. Recently, there has been a major development of architectures in CDI cells using carbon flow electrodes with membrane, called flow-electrode capacitive deionization (FCDI). In FCDI, the advantage is continuous desalination due to the carbon flow electrodes. Numerous research groups dedicated to develop the FCDI process, however, a clear pre-treatment of carbon flow electrodes was not suggested. Study herein, present a clear understanding of effects of pre-treatment of activated carbon based on sonication in the carbon flow electrodes for the basics results with respect to adsorption performance.