Broader contextDirect methanol fuel cells (DMFCs) are being considered as a possible solution to replace the current battery as the dominant power provider for portable electronic application, but they currently experience significant power density and efficiency losses due to high methanol crossover through proton exchange membranes (PEMs). Currently, Nafion® perfluorosulfonic acid (PFSA) membrane made by DuPont is the most frequently used PEM in DMFC. However, it is a poor barrier to methanol crossover, which limits its wide application in DMFC. In this communication, our synthesized PFSA polymers with a similar chemical structure to Nafion® were used as membrane materials, and PFSA membranes with various ion exchange capacities (IECs) from 0.36 mmol g−1to 1.17 mmol g−1were prepared. The relationship between the IECs of PFSA membranes and their transport properties (including water uptake, proton conductivity and methanol permeability) for DMFC applications was investigated.