In this paper, the ionic liquids 1,2-diethylpyridinium ethylsulfate, EEpyESO(4); 1-methylpyridinium methylsulfate, MpyMSO(4); 1,3-dimethylpyridinium methylsulfate, MMpyMSO(4); and 2-ethyl-1-methylpyridinium methylsulfate, EMpyMSO(4); were synthesized in our laboratory, and their experimental densities, speeds of sound, dynamic viscosities, and refractive indices were studied as a function of temperature at atmospheric pressure. Thermal expansion coefficient, molar volume, and molar refraction of these ionic liquids were calculated from the experimental density and refractive index values. (C) 2010 Elsevier Ltd. All rights reserved.