The speed of ultrasound measurements in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIm][NTf2], were performed in the temperature range from (288 to 318) K and at pressures from (15 to 101) MPa. The speeds of ultrasound, densities, and isobaric heat capacities have been determined at ambient pressure for temperatures from (287 to 323) K, (278.15 to 363.15) K, and (293.15 to 323.15) K, respectively. The pressure dependence of densities and adiabatic compressibilities were calculated using the speeds of ultrasound at high pressure as well as densities and heat capacities at ambient pressure. The experimental densities reported in the literature are in a good agreement with the densities calculated in this work.