In this work, experimental values of densities, refractive indices and speeds of sound for (n-nonane + tetraethylene glycol dimethyl ether (tetraglyme)) at temperatures from 288.15 K to 308.15 K and atmospheric pressure are presented as a function of mole fraction, The corresponding derived properties excess molar volumes, changes of refractive index, changes of speed of sound and changes of isentropic compressibilities on mixing were computed and variable-degree polynomials in mole fraction have been fitted to these results. Different mixing rules were applied in order to predict the refractive indices. The predictions are better when the volume change on mixing is considered. The binodal tie lines for the mixture at different temperatures were determined by the measurement of density and application of the corresponding fitting polynomials. The UNIQUAC method was applied to predict this (liquid + liquid) equilibrium.