The enthalpies of dilution and osmotic coefficients of ternary solutions of urea and α,ω-aliphatic diols in water have been determined at 298 K through microcalorimetric and vapour pressure osmometric measurements, respectively. The experimental virial coefficients of the power expansion series of the excess Gibbs energies and enthalpies have been evaluated and compared with the literature data for similar aqueous systems containing urea and alkanols, ketones and cyclic ethers. The following diols have been considered: propane-diol-1,3; butane-diol-1,4; pentane-diol-1,5. The results are discussed in terms of the hydrophilic and hydrophobic properties of the solutes, and in the light of previous data on the excess thermodynamic properties of binary water-aliphatic diol solutions.