A complete study of thermophysical properties concerning the 1,3-dimethyl-2imidazolidinone (DMI) + water binary system is realized. Density, speed of sound, dynamic viscosities, and refractive index measurements have been performed at atmospheric pressure, using a vibrating tube densitometer, a falling ball viscosimeter, and a refractometer for pure DMI, pure water, and for aqueous solutions of DMI, from 278.15 to 323.15 K. The thermal expansion was calculated from density data. Excess Gibbs energy of flow and the corresponding excess entropy of flow were also calculated considering dynamic viscosity and density data. Excess molar properties (volume, thermal expansion, Gibbs energy of flow and square of refractive index) were calculated and the Redlich-Kister equations were applied to correlate the data. The analysis of the behavior of the excess properties allows to identify the most relevant molecular interaction in mixtures rich in DMI and in mixtures rich in water. Our results show that DMI can be classified as a liquid structure maker and that molecules of water are certainly inserted in the DMI network at finite dilution.