Densities, speeds of sound, and electrical conductances in the aqueous solutions of room temperature ionic liquid, 1-hexyl-3-methylimidazolium bromide, [HMIm]Br were measured at temperatures T = (283.15 to 308.15) K and atmospheric pressure. Apparent molar volumes V-phi, isentropic compressibilities kappa(S), apparent molar isentropic compressibilitieS kappa(phi), and molar conductivities Lambda were determined. The corresponding limiting. apparent molar quantities were found by extrapolation to infinite dilution with using Redlich-Mayer equation. The obtained limiting apparent molar quantities at different temperatures indicate that (ion + solvent) interactions in the studied system. Limiting apparent molar expansibility E degrees(phi) values for aqueous solutions of this ionic liquid have a positive values. The value of (partial derivative V-2 degrees(phi)/partial derivative T-2)(P) was found small and negative which indicating the ionic liquid under study is predominantly a structure breaker. Isentropic compressibility isotherms intersect approximately at a concentration m = 1.5825 mol . kg(-1), which may be an indication of the structural interactions and clathrate formation. Calculated ion association constant K. values increase with increasing temperature show that the extent of ion association increases with increasing temperature. (c) 2008 Elsevier Ltd. All rights reserved.