Although sulfonated aromatic polymers are thought to be one of the promising materials for proton exchange membranes, most of them suffer from significant drop of proton conductivity with decrease in humidity. In this study, composite membranes composed of sulfonated poly(ether ether ketone) (sPEEK) and imidazole-functionalized silica (Si-Im) are prepared and humidity dependence of their proton conductivity is examined. The introduction of Si-Im to sPEEK facilitates intermolecular proton transfer as well as proton generation from sPEEK, resulting in improved proton conductivity at lower humidity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3615968] All rights reserved.