Proton exchange membranes for a Vanadium Redox Flow Battery(VRFB), based on polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene(SEBS), were modified to be more hydrophilic. First, SEBS-g-MA was synthesized by grafting maleic anhydride(MA) with SEBS. Then, SEBS-g-MA was sulfonated using chlorosulfuric acid and fabricated by solution casting. The addition of sulfonic acid group(-SO3H) and carboxylic acid group(-COOH) functionality was confirmed by FT-IR. The water uptake and ion conductivity of the membrane were higher compared to Nafion 117. After added SiO2 crossover phenomenon of V5 + ions become desrease. Atomic force microscopy analysis showed that the morphology of membrane surface which separation along with functionality. To increasing mechanical properties of membrane, cross-linking using sulfosuccinic acid(SSA).