In the present work, binary mixtures of 1-propyronitrile-3-hexylimidazolium bromide + methanol were prepared with different compositions and their density and refractive indices were measured at a temperature range (293.15 to 323.15) K and at atmospheric pressure. Thermal expansion coefficients were estimated using the measured density values. Excess molar volumes VE were calculated using the present experimental data and correlated using the Redlich Kister polynomial equation. © 2010 Elsevier B.V.