The dielectric response of aqueous sodium alginate solutions has been measured along with their viscosities at concentrations up to 5% m/v over the frequency range 10^–2–10⁴ Hz. The data were analysed by considering the systems to comprise a high-frequency bulk response in series with a low-frequency barrier response, reflecting the behaviour of an adsorbed alginate layer located at the electrodes. The effects of alginate concentration and the addition of calcium sulfate and diclofenac sodium have been investigated. The high-frequency capacitance and dielectric loss showed linear and logarithmic relationships with alginate concentration, respectively, and the low-frequency capacitance showed a plateau at a concentration corresponding to that at which an abrupt increase in viscosity was noted. Addition of calcium sulfate led to a considerable increase in viscosity but a much smaller change in dielectric response, while addition of the model drug diclofenac sodium resulted primarily in a change in dielectric response with little alteration in the viscosity.