Sulfonated poly(arylene ether sulfone) (SPAES) composite membranes were prepared using antioxidant grafted graphene oxide as a filler for polymer electrolyte membrane fuel cell (PEMFC) applications. SPAES was synthesized via condensation polymerization of 4,4'-dihydroxybiphenyl, 4,4'-dichlorodiphenylsulfone and 3,3'disulfonate-4,4'-dichlorodiphenylsulfone. The antioxidant grafted graphene oxide was prepared by grafting hindered amine, 4-amino-2,2,6,6-tetramethylpiperidine, onto the surface of graphene oxide (GO). The SPAES composite membrane containing the antioxidant grafted GO showed improved physicochemical properties such as mechanical strength, chemical and thermal stabilities, and proton conductivity compared to pristine SPAES membrane. In particular, the antioxidant grafted GO was much more effective in enhancing the chemical stability of SPAES than GO without the antioxidant. For example after Fenton's test, the SPAES composite membrane with grafted antioxidant showed smaller decrease of both the weight and proton conductivity values than the pristine SPAES and SPAES composite membrane with GO. The enhanced chemical stability of SPAES composite membrane with antioxidant grafted GO can be explained by the combined antioxidant effect of both grafted antioxidant functional groups and GO.