Binary mixtures of 1-hexyl-3-methylimidazolium bis(trisfluoromethylsulfonyl)imide hmimTf 2N with N-methyldiethanolamine (MDEA) were prepared. Physical properties namely, density �, dynamic viscosity η and refractive index n D, of the binary mixtures were measured over a temperature range of 303.15 K to 323.15 K. Excess molar volumes V E and excess refractive indices n D E were calculated from the experimental values and fitted to the Redlich-Kister equation. Viscosity values of binary mixtures were correlated by McAllister three body interaction model. Excess molar volumes showed positive deviations, whereas excess refractive indices showed negative values over the entire range of concentrations and temperatures. The coefficients of thermal expansion α, and excess coefficients of thermal expansion α E were also calculated from the experimental data. © 2012 Elsevier B.V.