Novel proton exchange membranes are solvent-cast from N,N-dimethylacetamide (DMAc) solutions of the crosslinked poly(arylene ether ketone) copolymer with pendant carboxylic acid group (C-SPAEK) via poly(ethylene glycol) (PEG) with different amounts. These membranes are formed as a result of physical and chemical crosslinking. In this study, H-1-NMR and FTIR have been used to confirm the chemical structures of the copolymers. Mechanical and thermal properties, swelling and proton conductivity are affected by the crosslinker (PEG) content in the copolymers. Compared to the noncrosslinked C-SPAEK membrane, the crosslinked membranes become more flexible and greatly reduced water uptake and swelling ratio with only slight sacrifice in proton conductivities. And the crosslinked membranes keep higher proton conductivities without a sharply decrease at higher temperature. These results show that the crosslinked membranes have potential applications as proton exchange membranes for fuel cell. (C) 2010 Wiley Periodicals, Inc. J Appl Po lym Sci 118: 3318-3323, 2010