The measurements of ultrasonic velocities (u), densities (r) and viscosities (h) of binary liquid mixtures of N-Ndimethylacetamide with acetone and acetonitrile have been carried out over the entire range of composition at temperature 298.15 K. Measured values are used to evaluated the other thermo dynamical parameters such as adiabatic compressibility (ba), free length (Lf), free volume (Vf) with their excess values as ba E, Lf E and Vf E. From the properties of these excess parameters the nature and strength of the interactions in these binary systems are discussed. The non linearity found in all the plots of these ultrasonic parameters and their excess values for the composition range indicates presence of the intermolecular interaction between the components of the unlike molecules of the mixture.
