Sodium metaphosphate-based glasses (mol%) (100-x) NaPO3-xNa2SO4 (0 <= x <= 25), were prepared by melt quenching technique. The influence of Na2SO4 additives on the thermal, physical and structural properties has been interpreted using density, DSC, ultrasonic velocity and FTIR data. The linear decrease in glass transition temperature (T-g) with increase in Na2SO4 content indicates decrease in average chain length of the host glass matrix. FTIR data has revealed that Na2SO4 has depolymerized the phosphate glass matrix. The temperature-dependent conductivity data of the above glass samples have been obtained using impedance measurement in the temperature range 400-5 10 K. The sigma T products for all the glass compositions have obeyed an Arrehenius relationship, exhibiting an activation energy of about 0.70 eV for ion migration. The ionic conductivity of the host glass, NaPO3 with a value of 1.1 x 10(-6) S cm(-1) has been enhanced by one order of magnitude to a value of 9.4 x 10(-6) S cm(-1) for the glass with maximum content of Na2SO4 at 450 K. Enhancement in the ionic conductivity has been explained on the basis of dissociation of Na2SO4, resulting in the enhancement of the charge carrier concentration. Electronic transport number of a value 0.01 determined by the dc polarization technique and ionic transport number of a value 0.94 measured by the emf method indicate the ionic nature of the conducting species. (c) 2007 Elsevier B.V. All rights reserved.