The ultrasonic speed (U) studies are carried out using single crystal variable path fixed frequency (2 MHz) ultrasonic interferometer on some aliphatic amines (Propylamine, PA, Butylamine, BA, dipropylamine, DPA) in N-methyl-2-pyrrolidone (NMP) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. To examine the intermolecular interactions in these liquid mixtures ultrasonic speeds are theoretically evaluated based on scaled particle theory and compared with the experimentally measured values. An attempt is made to study the temperature effect on the shapes of the interacting molecules in the binary liquid mixture using scaled particle theory in the temperature range 303.15-318.15 K.