The state of water in fully hydrated sulfonated poly(ether ether ketone) - silica hybrid proton exchange membranes were characterized in terms of the exchange rate between bound and free water, the water dynamics in each phase, and the relative water populations by H-1 ODESSA and transverse magnetization relaxation NMR. The exchange rate, the amount of bound water, and the reorientation of free water molecules increase in the presence of silica particles. The dynamics of bound water was described by the Levy statistics with a Cauchy propagator. The proton exchange membranes performances could be improved by addition of small concentrations of silica in the range of 5-10 wt.%. (C) 2009 Elsevier B.V. All rights reserved.