Membranes based on new sulfonated poly(arylene ether sulfone)-b-polybutadiene (SPAES-b-PB) block copolymers were prepared by solution casting method. Epoxidation of the membranes at PB blocks of copolymer was conducted by an in situ generated peracid method. The kinetic of epoxidation process was studied by Fourier transform infrared spectroscopy (FTIR). Notable changes of microstructure and surface morphology of membranes were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). We found that the tensile strength and the thermal decomposition temperature of epoxidized membranes were higher than those of unepoxidized membranes, and they increased remarkably with increasing the degree of sulfonation (DS). The proton conductivity of epoxidized membrane with DS of 15.7% was higher than that of unepoxidized sample at all testing temperatures and reached 1.43 x 10(-1) S/cm at 90 degrees C. All these property changes occurred due to epoxidation modification which induced rearrangements and uniform distributions of hydrogen bonds intra and inter macromolecular chains to form channel-like phase separated microstructure. (c) 2005 Elsevier B.V. All rights reserved.