This paper presents experimental data for densities (p) and ultrasonic speeds (u) of pure styrene and toluene and of their binary liquid mixtures over the entire composition range at 298.15, 303.15, 308.15 and 313.15 K. From the experimental data the excess molar volumes (V E ), deviations in isentropic compressibilities (Δk s ), and in acoustic impedances (ΔZ), were calculated for the binary mixtures over the entire composition range at all the temperatures. Moreover, partial molar volumes, V 0 φ,1 and V 0 φ , 2 and partial molar isentropic compressibilities, K 0 φ,1 and K 0 φ,1 at infinite dilution of styrene in toluene and toluene in styrene were examined. The variations of these parameters with composition of mixture suggest the strength of interactions between the component molecules under study.