Polyphenylsulfone was sulfonated by two different methods: reaction with SO3 and reaction with (CH3)(3)SiSO3Cl. The products were characterized, and the advantages of both methods are discussed. Much more homogeneous products were obtained from the reaction with (CH3)(3)SiSO3Cl, along with better control of the sulfonation degree. An alternative method of membrane preparation led to an asymmetric structure, which allowed the combination of high mechanical stability and high proton conductance.