Abstract: Epoxidized polysulfone (OPSF) was prepared by incorporating epoxy group into the backbone of polysulfone (PSF) via Friedel-Crafts alkylation reaction with epoxy chloropropane, and then a novel type of sulfonated polysulfone with the side chain of naphthalene sulfonic acid (PSF-NS) was obtained by the reaction of OPSF with 2-naphthol-6,8-disulfonic acid dipotassium. The chemical structure of PSF-NS was characterized by FT-IR and 1H-NMR spectroscopy, and the corresponding proton exchange membranes (PEMs) were prepared by a solution casting method. The effects of temperature on the performance including ion exchange capacity, water uptake, swelling ratio and proton conductivity of PEMs were studied extensively. The experimental results indicated that the resulting PEMs exhibit an excellent dimensional stability at a high water-sorption rate compared to other types of side chain aromatic PEMs. The water uptake, swelling ratio and proton conductivity of PEMs increased with an increase of temperature. The water uptake of the PEMs with a sulfonated group amount of 1.43 mmol/g was 29.6 wt% and 43.1 wt% at 25 and 85 ℃, respectively, and the corresponding swelling ratios were 25.2 % and 56.2 %. Its methanol permeability was only 16.8×10-7 cm2/s, which was lower than that of Nafion115 membranes at the same condition.