Proton conductivity of Nafion membranes, the key feature for their application in proton exchange membrane fuel cells, has been reported in many works. It becomes necessary to assemble these massive reports to present an overview for further development guidelines. We apply an exhaustive search and retrieve 3539 records from 310 original reports. These records are dumped into a database and a statistical analysis is carried out to establish the overview. The histogram, the trend, the temperature, the relative humidity and fillers related to the proton conductivity of Nafion membranes are investigated. There is not always positive progress in recent 13 years to improve the proton conductivity of Nafion membranes. The proton conductivity can be fitted using a simple exponentially increasing function for relative humidity dependence, and the Arrhenius equation for temperature dependence with acceptable correlation confidence. Water contents in membranes from vapor can be well depicted by Brunauer-Emmett-Teller equation, and they have reasonable correlation with proton conductivities. Inorganic fillers usually provide better enhancement in proton conductivity than organic fillers, which is a result of the former have better water-holding capability. Fillers that can facilitate the formation of percolated water channel with less tortuosity have high probability to significantly improve the proton conductivity of Nafion membranes. (C) 2016 Elsevier B.V. All rights reserved.