Polystyrene (PS) is a synthetic aromatic hydrocarbon polymer prepared from the monomer styrene. Polystyrene can be foamed or solid. General-purpose polystyrene is hard, clear and rather brittle. It is a low cast resin per unit weight. It is a rather poor barrier to oxygen and water vapour and has a relatively low melting point. Polystyrene is one of the most widely used plastics, the scale of its production being several million tonnes per year. Polystyrene can be naturally transparent, but can be coloured with colourants. Uses include protective packaging (such as packing peanuts and DVD and CD cases), bottles, trays, containers, lids, tumblers, disposable cutlery and in the making of models. In the present study an attempt has been made to compute the viscosity of Polystyrene (M.W: 35000) in toluene and 1,4-Dioxane at different concentrations (0.2%, 0.4%, 0.6%, 0.8% __ampersandsignamp; 1.0%) at different temperatures (303 K, 308 K, 313 K __ampersandsignamp; 318 K). From these experimental data, activation energy is calculated and the effect of solvent is analyzed. Density and ultrasonic velocity have been estimated for the above systems at 303K. From these experimental values, various molecular interaction parameters like free volume, internal pressure, viscous relaxation time, inter-atomic free length, etc. are calculated and discussed in terms of solute-solvent interactions.