When fine-sized 45ZnO·55P2O5 glass powders were mixed with water, hydration immediately occurred, resulting in the formation of a viscous hydrogel. 31P MAS-NMR spectra showed that the hydrogel contains orthophosphates and long polyphosphates. 45ZnO·55P2O5 glass-derived hydrogel (45ZP gel) showed high conductivities of 9.9 mS/cm at 30 °C. The conductivities were related to the proton amount in the hydrogel. The electric double-layer capacitor (EDC) cell for the 45ZP gel showed no oxidation-reduction processes in the range of 0~1 V and the specific capacities of 2.40 F/g. The possibility as an EDC electrolyte may be related to the conductivities of the hydrogels.