Electrical properties of vanadium pentoxide hydrate were studied by impedance measurements. Of the intrinsic samples prepared by the ion-exchange polymerization method, an ionic conduction predominates over electronic conduction at around the relative H2O vapor pressure of 0.1, i.e., at the monolayer adsorption of H2O molecules, and increases to 80% of the total conductivity at higher H2O vapor pressures. Impedance analysis of the system indicated that H2O molecules are adsorbed in two modes at a humidity of P/P-0 < 0.4, one of which restricts the motion of H2O molecules and eases with increased humidity up to P/P-0 = 0.4 to have H2O molecules relax similarly to the other mode having a smaller relaxation time for H+ hopping. Partial reduction of V5+ to V4+ in the solid phase increased the contribution of electrical conductivity to about 90% of the total conduction in the lower humidity range up to P/P-0 = 0.5. Rotational motion of H2O molecules in this range is easier than that in the intrinsic material. At higher humidity giving double H2O layers, however, H2O molecules adsorbed are ordered between the layers. The model of dynamic properties of H2O in the reduced sample was supported by the observation of a spectral shift in the FT-IR spectra.