The densities, rho, speeds of sound, u and refractive indices, n(D) of binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide {[Bmim][NTf2]} and N-methyl-2-pyrrolidinone (NMP), including those of pure liquids, over the entire composition range were measured at temperatures (298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K and atmospheric pressure. From the experimental values, the excess molar volumes, V-m(E), excess isentropic compressibilities, K-s(E), excess speeds of sound, u(E), deviations in refractive index, D/n(D) and deviations in molar refraction, Delta R-M have been calculated. The partial molar volumes, (V) over bar (m,1) and (V) over bar (m,2) and excess partial molar volumes, (V) over bar (E)(m,1) and (V) over bar (E)(m,2) over the whole composition range and the partial molar volumes, (V) over bar (degrees)(m,1) and (V) over bar (degrees) (E)(m,2) and excess partial molar volumes, (V) over bar (degrees)(E)(m,1) and (V) over bar (degrees)(E)(m,2) of the components at infinite dilution have also been calculated. The variations of these parameters with composition and temperature have been discussed in terms of intermolecular interactions prevailing in these mixtures. (C) 2016 Elsevier Ltd. All rights reserved.