The phosphonic acid cation exchange membrane (CEM) was prepared by plasma-induced grafting of phosphonated glycidyl methacrylate, and its properties were compared with those of sulfonated acid CEM. Although ion exchange capacity and water content of the phosphonic and sulfonic acid CEMs are almost same, the electrical resistance of the phosphonic acid CEM was higher and the transport number was slightly lower compared to the sulfonic acid CEM due to weakly acidic fixed ionic charges. However, those properties of the phosphonic acid CEM were comparable with those of the membranes reported in literature. Current-voltage curves of the membranes showed that the strong fixed charge of sulfonic acid CEM induced more electroconvection of electrolyte near the surface over the limiting current density than phosphonic acid CEM with weaker fixed charge.