For application in fuel cells, a series of low-cost proton exchange membranes with covalently crosslinking structure were prepared from sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) just through a heat treatment. The crosslinking reaction was verified and investigated in detail. The crosslinking degree could be controlled by adjusting the time or temperature for heat treatment. With a proton conductivity of 0.128 S cm(-1) and tensile strength of 52.8 MPa, the optimum membrane showed a maxim power density of 0.893 W cm(-2) while that of Nafion (R) 112 is 0.602 W cm(-2) in a single cell test at 60 degrees C. In view of the competitive properties with Nafion (R) series, the crosslinked membranes are qualified for a potential application in fuel cells. (C) 2009 Elsevier B.V. All rights reserved.