An ion exchange membrane for a redox flow battery, the anion exchange membrane including a porous substrate; and a polymer disposed in the porous substrate, wherein the polymer is a polymerization product of a composition for forming the ion exchange membrane, wherein the composition includes a first monomer and a second monomer, wherein the first monomer is substituted with a group including an ethylenic unsaturated double bond and includes a cationic heterocyclic compound including a nitrogen heteroatom and a counter anion thereof, and wherein the second monomer is polymerizable with the first monomer and is at least one selected from a (meth)acrylamide compound and a (meth)acrylate compound.