In this work, we explore and compare the role of the ion effect on the thermophysical properties of two families of ionic liquids (ILs), namely, tetra-alkyl ammonium cation [RINT] with hydroxide [OH] anion and 1-alkyl-3-methyl imidazolium cation [amim](+) with different anions (chloride, methyl sulfate, and tetrafluoroborate), with polar solvent such as dimethylsulfoxide (DMSO) in the temperature range from 25 to 40 degrees C and over the whole concentration range of ILs. Two families of ILs, namely, tetramethyl ammonium hydroxide [(CH3)(4)N[OH] (TMAH), tetraethyl ammonium hydroxide [(C2H5)(4)][OH] (TEAH), tetrapropyl ammonium hydroxide [(C3H7)(4)N][OH] (TPAH), and tetrabutyl ammonium hydroxide [(C4H9)(4)N][OH] (TBAH) from ammonium-based ILs and 1-ethyl-3-methylimidazolium chloride [Emirn][Cl], 1-ethyl-3-methylimidazolium methylsulfate [Emim][MeSO4], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim] [BF4], and 1-butyl-3-methylimidazolium chloride aBmirn][Cl]) from imidazolium family of ILs, are used in the present study. To address the molecular interactions of ILs with DMSO, densities (rho), ultrasonic sound velocities (u), and viscosities (eta) have been measured over the entire composition range and at four temperatures, 25, 30, 35, and 40 degrees C, under atmospheric pressure. From these experimental data, the excess molar volume (V-E), the deviation in isentropic compressibility (Arc), and the deviation in viscosity (Delta eta were calculated and were adequately correlated by using the Redlich-Kister polynomial equation. The measured and predicted data were interpreted on the basis of intermolecular interactions and structural effects between like and unlike molecules upon mixing. The hydrogen-bonding features between ammonium-based ILs and DMSO were analyzed using molecular modeling program by HyperChem 7.