The application of electrodialysis (ED) for desalination requires the use of natural seawater or river water, in which the presence of multivalent ions is inevitable. This currently limits the process performance. Membranes with selectivity for monovalent ions may overcome this limitation. This study used the method of electro-deposition with chitosan/aniline polymer as a modification material to coat a commercial anion exchange membrane in view of obtaining selectivity for monovalent ions. Chitosan was grafted with polyaniline through copolymerization using ammonium persulfate as an initiator. FTIR spectra of the composites revealed that there was a strong interaction between substituted polyanilines and chitosan. The method was used to prepare a series of membranes by varying the aniline ratio and polymerization time. The chemical composition and surface properties of the membranes were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. Current–voltage curves and resistance were measured to characterize the transport properties of the membranes and the membrane conductivity. The results show that the membrane conductivity increases with the aniline ratio; the selectivity initially increases with the aniline ratio, and then decreases again. The optimum modification condition was an electrodeposition time of 4 h with an aniline ratio of 0.4. Using the modified membrane in concentrated sea water, it was demonstrated that the modified membrane has an excellent selectivity towards monovalent cations.