Conductivities, densities and speeds of sound of 1-butyl-2,3-dimethylimidazolium chloride in aqueous solutions were measured at 15, 25, and 35 degrees C. These data have been used to characterize the aggregation process of imidazolium based ionic liquid in the aqueous solution. The critical aggregation concentration (cac) and the degree of ionization, alpha, were determined by conductivity measurements. Both quantities were used to calculate the standard free energy change of aggregation, Delta G(a)(0). It shows decrease in alpha and Delta G(a)(0) upon growth of temperature. From density data for the ionic liquid, the apparent molar volume, V-phi. was calculated. The adiabatic compressibility, beta(s), changes in adiabatic compressibility upon aggregation, Delta beta(s.agg), and apparent adiabatic compressibilities, beta(phi,s), were calculated from measurements of density and ultrasound velocity. Good agreement has been found when comparing with the aggregation properties of 1-butyl-2,3-dimethylimidazolium chloride both from conductivity and molar volume approach. (C) 2013 Elsevier B.V. All rights reserved.