Binary mixtures of 1-hexyl-3-methylimidazolium tetrafluoroborate hmimBF4 with N-methyldiethanolamine (MDEA) were prepared. Physical properties namely, density �, dynamic viscosity η and refractive index nD, of the binary mixtures were measured over a temperature range of 303.15 K to 323.15 K. The measured density and refractive index data were correlated as a function of concentration and temperature. Excess molar volumes VE were deduced from the experimental data. Excess molar volumes showed positive deviations over the entire range of concentrations and temperatures indicating a weak interaction between hmimBF4 and MDEA. Viscosity data for the binary mixtures were correlated by using the Kendall-Monroe model. © 2012 Elsevier B.V. All rights reserved.