Hydrated Na ions have been ion-exchange intercalated into the insulating layered cadmium thiophosphate to give Cd0.75PS3Na0.5(H2O)(y). Intercalation occurs with a dilation of the lattice which depends on the extent of hydration of the interlamellar Na ion; for y = 1 the lattice expansion is 2.8 Angstrom, while for y = 2 it is 5.5 Angstrom. The conductivity and dielectric response of Cd0.75PS3Na0.5(H2O)(y), y = 1, 2, have been investigated as a function of frequency and temperature. The electrical behavior of the two compounds is dramatically different. In the y = 2 compound Na ions are mobile and the material is conducting. The dielectric spectrum is featureless, but the electrical modulus, the reciprocal of the complex dielectric permittivity, exhibits a conductivity relaxation. In contrast, when y = 1, the compound is nonconducting, with the dielectric permittivity exhibiting a relaxation. The relaxation times and activation energy are comparable to that of the dielectric relaxation at acoustic frequencies in ice.