Sulfonated poly(bis-A)-sulfone (SPSF) samples were prepared by a mild postsulfonation method using trimethylsilyl chlorosulfonate as sulfonation agent, and their thermal and mechanical properties were evaluated. The serials of SPSF membranes are thermally stable up to 450 degrees C in air. When compared with the poly(bis-A)-sulfone membrane, the hydrophilicity and water uptake of the SPSF membranes are enhanced. A microphase-separated structure comprised of hydrophilic and hydrophobic polymer backbone was observed from atomic force microscopy phase images. The hydrophilic ionic clusters become continuous to form channels when ion exchange capacity (IEC) reached 1.47 mequiv/g. Moreover, the membranes showed very good proton conductivities (20 degrees C, 0.01-0.11 S/cm) and low-methanol permeability (0.09-3.06 x 10-6 cm(2/)s) and the methanol diffusion coefficients were lower than that of Nafion112 (1.35 x 10-6 cm(2)/s) with IEC values from 0.70 to 1.47 mequiv/g. However, the Fenton's reagent test revealed that the membranes exhibited very poor oxidation stability, which is the main defect limiting the application of SPSF for proton exchange membranes. POLYM. ENG. SCI., 51:264-271, 2011. (C) 2010 Society of Plastics Engineers