Water saturated shaly sandstones exhibit a strong dielectric dispersion at frequencies below 106 Hz, that is mainly related to the ionic diffusion in the electrolyte surrounding the clay particles. Assuming a coupled electro-diffusional mechanism occurring in a Guoy-Cbapman double layer, we derived analytical expressions for the effective conductivity and permittivity of a charged spherical particle immersed in an electrolytic solution. Introducing these equivalent homogeneous properties into generalized mixture theories we can simulate the behavior of shaly sands at different water saturations. The effective bulk properties of a mixture containing clays are shown to be strongly dependent on a clay parameter ?1 /??(where??1 is the fixed charge density and ? the particle radius), and also on the conductivity of the electrolyte. We have studied in detail the dependence on the free electrolyte conductivity ??, at some frequencies at which logging tools are available. The behavior of the effective conductivity shows a nonlinear increase with ?? at dilute concentrations, tending to a linear relation at high ?? , in conformity with many experimental observations, Conversely, the effective dielectric constant may behave as a decreasing function of ?? . Such a relationship can be modified, however, depending on the salinity of the water inside the shale component. The effects of partial water saturation were also modeled using a three component self-similar mixture of conducting solids, oil droplets and water. The results compare satisfactorily with available experimental data, using reasonable parameters for the clays. The water conductivity and saturation effects in shaly sands at various frequencies are discussed from the point of view of their applicability to various logging tools from 10Hz to 25MHz.