In this work, a new series of low viscous protic ionic liquids based on N-methylpyrrolidone cation and carboxylate anions with different chain length has been synthesized and characterized. Density, speed of sound and viscosity have been measured for these ionic liquids in the temperature range from 293.15 to 343.15 K. The density data have been fitted to linear equation as well as correlated with group contribution method developed by Gardas and Coutinho. From the density correlation, molecular volume data for cation and anion constituents of studied ionic liquids have been proposed. By using experimental density and speed of sound data, the isentropic compressibility, coefficient of thermal expansion, standard entropy, intermolecular free length and lattice energy have been calculated for studied ionic liquids. Viscosity data were correlated with the Vogel-Tammann-Fulcher equation. To understand the nature of the ionic liquids and structure-property relationship, the effect of anion alkyl chain length has been studied and correlated. Ionic liquids studied in this work are comparatively cheaper in price and can be promising in bio-macromolecule solubilization and other commercial fields. (C) 2014 Elsevier B.V. All rights reserved.