Dielectric properties, permittivities and losses, of the SrF2-H2O system in which two-dimensional condensation of water occurs were investigated as a function of surface coverage at 298, 273, and 230 K and in the frequency range from 0.1 Hz to 5 MHz. In this system large dielectric dispersions were observed at 298 K near 0.3 and 15 Hz and at coverages of 0.13 and 1.26 monolayers, respectively. Some experiments were carried out to elucidate these relaxations. It is concluded that these relaxations are due to interfacial polarization arising from heterogeneity of the system, i.e., Maxwell-Wagner type, and not to orientational polarization of the adsorbed water, namely Debye type. The former polarization is explained by a two-layer model based on the difference in conductances between the electrode-particle and the particle-particle. The conductance varies with the amounts of adsorbed water, and the mechanism of conduction in the adsorbed layer is interpreted in terms of Grotthus’ mechanism. Moreover, it is found that the two-dimensionally condensed water causes a small change in the conductance. The adsorbed state of water on the SrF2 surface is discussed on the basis of experimental data.