Binary xMO center dot(100 - x)P2O5 (mol%; M = Ca, Mg) glasses were prepared using a conventional melting method, and the proton conduction mechanism in the glasses was investigated. The proton conductivities of the glasses were measured under various hydrogen (H-2) gas concentrations from 0 to 100 vol.% using Pt electrodes. The CaO center dot P2O5 glasses show higher proton conductivities than MgO center dot P2O5 ones. Fourier-transform infrared (FTIR) measurements showed that protons dissociated from H-2 gas at the Pt electrodes are incorporated into the glasses, and the proton conductivity increases as a result of an increase in the carrier (proton) concentration. There is a good linear relationship between the peak wavenumber of P=O-nb (O-nb indicates non-bridging oxygen) and the proton conductivity measured in a 100 vol.% H-2 atmosphere. Furthermore synchrotron radiation X-ray diffraction (SRXRD) and FTIR results suggest that the pi-electron of P=O double bond is localized significantly in MgO center dot P2O5 compared with CaO center dot P2O5 glasses, which is the origin of higher proton conductivity in CaO center dot P2O5 glasses. (C) 2013 Elsevier B.V. All rights reserved.