Composite membranes formed by sulfonated poly-ether-ether-ketone (SPEEK) and sulfonated and/or silylated poly-phenyl-sulfone ((Si,S)PPSU) were prepared. (Si,S)PPSU was used as anchor phase to reinforce membranes based on SPEEK with high degree of sulfonation, which is proton conducting but morphologically unstable. The ionomer membranes were characterized by several techniques, including high resolution thermogravimetric analysis, static and dynamic mechanical measurements, water uptake by immersion and in vapour phase. Properties of hybrid blends with 93 wt% SPEEK and 7 wt% of (Si,S)PPSU were compared to those of pure SPEEK. Thermal properties are discussed in view of ionomer composition. The presence of bulky phenyl-silanol groups leads to an evident reduction of water uptake and greatly enhanced mechanical strength. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.