In this paper, original hybrid organic/inorganic membranes based on a poly(vinylidenefluoride-co-hexafluoropropylene) polymer associated with mesostructured modified silica and made through sol-gel techniques were characterized by using cyclic electrogravimetry and ac electrogravimetry. To perform these experiments, a polypyrrole-heteropolyanion doped mediator film was generated between the working electrode of the microbalance and the hybrid membrane (HM). This mixed conductor mediator film is necessary to provide proton transfer between the different interfaces and, therefore, proton transport inside the HM, which is only an ion conductor. These coupled techniques, due to their extraordinary sensitivity and precision, constitute an indirect way of understanding the H+ insertion (at the interfaces)/diffusion (through the HMs) behavior of the HMs, where the H+ transport is complex. Complementary to the ionic conductivity values, the characterization of the HMs with these novel techniques can explain the modest proton conduction and can determine if the limiting mechanism is the proton insertion or diffusion. Therefore, it represents a useful tool for studying the proton conduction mechanisms and, consequently, for designing HMs with low ohmic losses. These techniques can be extended to other proton exchange membrane fuel cell membranes and can constitute a general tool for characterizing the materials where the insertion of H+ induces charge transfer. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3421969] All rights reserved.