Highly permeable and selective membranes are desirable for mono/divalent cations separation. Here, we report the fabrication of a novel monovalent cation perm-selective membrane (MCPM) for selective cations separation via electrodialysis. The selective layer was fabricated via interfacial polymerization of ethylenediamine, tetraethylenepentamine and polyethyleneimine with 1,3,5-benzenetricarbonyle trichloride on the hydrolyzed polyacrylonitrile porous substrate. The negatively charged porous substrate and ultrathin polyamide selective layer could offer multidimensional channels for ions transport. In addition, the transport of large-sized Mg2+ was greatly intercepted by the compact polyamide selective layer, thus the perm-selectivity was significantly improved. High perm-selectivity (P-Mg2+(Na2+) = 3.3) which is 94% higher than that of a commercial MCPM was obtained, meanwhile it maintained good Na+ flux (J(Na+) = 4.27 x 10(-8) mol cm(-2) s(-1)) at a current density of 14 mA cm(-2). Furthermore, such unique structure also lead to high limiting current density and excellent long-term stability.