Phosphate glasses are promising materials for electrolytes of intermediate temperature fuel cells, because they have good proton conductivity at 150-250 degrees C. However, the effects of the glass composition and melting condition on proton conductivities are unclear yet. In this work, the structures of BaO-ZnO-P2O5 glasses were investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR) and Raman spectroscopy, and the proton conductivities were measured by an AC impedance method. The proton conductivity of 30 mol%ZnO-70 mol%P2O5 glass melted at 800 degrees C reached 1 x 10(-3) S/cm at 250 degrees C for. The proton transportation number of the ZnO-P2O5 glass was almost unity, confirmed by a hydrogen concentration cell. The power density of 0.4 mW/cm(2) was obtained for a fuel cell using the ZnO-P2O5 glass electrolyte at 250 degrees C. A branching phosphate structure was transformed into a middle phosphate structure by substituting BaO with ZnO, which caused an improvement in proton mobility. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.