Excess molar volumes (V-E) and ultrasonic studies at T = 303.15 K and atmospheric pressure have been measured over the whole composition range for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with ketones. Tire ketones studied in the present investigation include methyl ethyl ketone (MEK), diethylketone (DEK), methyl propyl ketone (MPK), methyl isobutyl ketone (MIBK), and cyclohexanone (CH). The V-E values were measured using a dilatometer and were negative over the entire mole it action range for NMP with MEK, DEK, MPK, and MIBK and were positive for NMP with CH. The ultrasonic sound velocities for the above systems were measured with a single crystal interferometer at a frequency of 3 MHz. The sound velocity (u) results have been used to calculate isentropic compressibility (K-s) and deviation in isentropic compressibility (Delta K-s) over the entire range of volume fraction. The Sound velocity results have been predicted in terms of free length theory (FLT), collision factor theory (CFT), and Nomoto relation, The results reveal that all the theories gave a satisfactory estimate of the sound velocity. The deviation values of the isentropic compressibilities (Delta K-s) were negative over the entire range of volume fraction in all the binary liquid mixtures except in the binary system NMP with CH, where we observed positive Delta K-s values. The results are interpreted on possible molecular interactions between components. (C) 2009 Elsevier Ltd. All rights reserved.