Sodium borosulfate glasses having composition xNa 2SO 4·(30− x)Na 2O·70B 2O 3 (1.5 ≤ x ≤ 9.0 mol%) were prepared by melt-quenching technique. The influence of Na 2SO 4 on physical and thermal properties has been interpreted using density, molar volume and DSC data. The decrease in glass transition temperature ( T g) with increase in Na 2SO 4 content indicates that the average chain length of the host glass matrix decreases. The temperature-dependent conductivity data of the above glass samples have been obtained using impedance measurement in the temperature range 523–593 K and the frequency range 20 Hz to 1 MHz. The dc electrical conductivity ( σ dc) follows Arrehenius relationship and activation energy is 0.83 ± 0.03 eV for ionic migration. The dc conductivity (at 553 K) of the glass with x = 1.5 mol% is 2.08 × 10 −4 Ω −1 m −1 and it is 6.16 × 10 −4 Ω −1 m −1 for x = 9 mol%. The ac conductivity obeys Almond-West type power law behaviour: σ( ω) = σ dc + σ ac( ω) = σ dc + A ω s. The behaviour of the complex permittivity, dielectric loss and dielectric modulus as a function of frequency was also investigated. An excellent time–temperature superposition in the imaginary part of dielectric modulus ( M″) confirms that the dynamical processes are temperature independent and is also an indicative of a common ion transport mechanism.