A novel graft copolymer consisting of a poly(vinylidene fluoride-co-chlorotrifluoroethylene) backbone and poly (glycidyl methacrylate) side chains, that is, P(VDF-co-CTFE)-g- PGMA, was synthesized through atom transfer radical polymerization (ATRP) using CTFE units as a macroinitiator. Successful synthesis and microphase-separated structure of the polymer were confirmed by 1H NMR, FTIR spectroscopy, and TEM. Assynthesized P(VDF-co-CTFE)-g-PGMA copolymer was sulfonated by sodium bisulfate, followed by thermal crosslinking with sulfosuccinic acid (SA) via the esterification to produce grafted/crosslinked polymer electrolyte membranes. The IEC values continuously increased with increasing SA content but water uptake increased with SA content up to 10 wt %, above which it decreased again as a result of competitive effect between crosslinking and hydrophilicity of membranes. At 20 wt % of SA content, the proton conductivity reached 0.057 and 0.11 S/cm at 20 and 80 ° C, respectively. The grafted/crosslinked P(VDF-co-CTFE)- g-PGMA/SA membranes exhibited good mechanical properties (>400 MPa of Young's modulus) and high thermal stability (up to 300 ° C), as determined by a universal testing machine (UTM) and TGA.