In the present paper, the ionic conductivity and the dielectric relaxation properties of Na2SO4 have been investigated by means of impedance spectroscopy measurements over wide ranges of frequencies and temperatures. The frequency dependent impedance data has been modeled by appropriate equivalent circuit representing the bulk and grain boundary properties of the sample. Phase transition temperatures and the activation energies of conduction in different phases have been determined from the temperature dependence of the dc conductivity. Dielectric relaxation has been studied using the complex electric modulus and permittivity formalisms. From the electric modulus formalism it is concluded that the relaxation mechanism is independent of temperature. The dielectric permittivity spectra were analyzed by the Cole-Cole formula where different parameters are determined. (c) 2005 Elsevier B.V. All rights reserved.