The influence of the addition of N-ethyl-2-pyrrolidone to the system monoethanolamine + water upon several physical properties has been studied in the present work. Density, speed of sound, and viscosity were determined for the tertiary mixture monoethanolamine (MEA) + water + N-ethyl-2-pyrrolidone (NEP), for NEP mass fraction lower than 0.3. These properties were obtained at different temperatures from (293.15 to 323.15) K and at atmospheric pressure. The excess molar volumes and isentropic compressibility were also calculated.