In this study, composite cation exchange membranes (C-CEMs) based on polyvinyl pyrrolidone (PVP) and mainchain sulfonated polyethersulfone (SPES) were prepared by adding conducting polyaniline (PANi). The electrodialysis (ED) properties of these C-CEMs were characterized to determine their feasibility for practical applications. C-CEMs exhibited smooth surfaces and dense cross-sections when PANi was homogeneously dispersed in the matrix material. An increase in C-CEM mechanical stability was attributed to the formation of a crosslinked structure. The experimental results showed that C-CEM with 0.6% PANi possessed the highest ionic conductivity. ED process results showed that C-CEM with 0.6% PANi exhibited better desalination properties than those of other C-CEMs and commercial CEM. On the whole, an appropriate PANi content improved C-CEM desalination properties. This study detailed a new method for the preparation of novel, low-cost C-CEMs with improved properties. It was found that a 0.6% PANi content was optimal for improving membrane performance.