In this article, novel branched sulfonated poly(ether ether ketone)s (Br-SPEEK) containing various amounts of 1,3,5-tris(4-fluorobenzoyl)benzene as the branching agent have been successfully prepared. Compared with the traditional linear polymer membranes, the membranes prepared by Br-SPEEK showed improved mechanical strength, excellent dimensional stability and superior oxidative stability with similar proton conductivity. Notably, the Br-SPEEK-10 membrane began to break after 267 min in Fenton's reagent at 80 C, which was 4 times longer than that of the L-SPEEK. Although the proton conductivity decreased with the addition of the branching agent, satisfying methanol permeability value was observed (down to 6.3 x 10(-7) cm(2) s(-1)), which was much lower than Nafion 117 (15.5 x 10(-7) cm(2) s(-1)). All the results indicated that the novel branched sulfonated poly(ether ether ketone)s membrane was potential candidate as proton conductive membranes for application in fuel cells. Crown Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.