The measured densities,, and speeds of sound, u, for pure ethyl propionate (EP) and m-xylene from (298.15 to 323.15) K and their binary mixtures have been reported. Excess internal pressure ( iE), excess free length (LfE), excess free volume (VfE), excess enthalpy (HE), excess free energy (GE) and excess entropy (TsE) for binary mixtures were determined. The calculated excess values have been fitted to the Redlich-Kister polynomial equations and the results are analysed in terms of molecular interactions due to physical, chemical and structural effects between the unlike molecules.