The branched sulfonated poly(ether ether ketone)s, derived from bisphenol fluorene, 1,1,1-tris(4-hydroxyphenyl)ethane, sulfonated difluorobenzophenone and 4,4'-difluorobenzophenone, were synthesized by potassium carbonate mediated nucleophilic polycondensation reaction. The highly branched sulfonated polymer/antioxidant composites were prepared using antioxidant 1010 as a functional additive in order to further improve the properties of the polymer. The composites were soluble in the polar organic solvents, such as NMP, DMAc, DMSO and DMF, and could be readily cast to form tough and smooth films. The membranes exhibited excellent oxidative stability, good proton conductivity and thermal stability. The maximum oxidative stability of the membranes with 5 wt% antioxidant was about 1.5 times larger than that of the sample without the antioxidant. The results showed that adding the antioxidant was an effective way to improve oxidative stability of the membranes. (C) 2011 Elsevier B.V. All rights reserved.