Densities, viscosities, and refractive indices of binary liquid mixtures of diethyl oxalate (DEO) with four ketones (acetophenone, cyclopentanone, cyclohexanone, and 3-pentanone) were determined over the complete concentration range at (303.15, 308.15, and 313.15) K. The experimental values of mixtures and pure liquids have been used to calculate the excess molar volumes, deviations in viscosity, and deviations in molar refractions. These excess or deviation properties were fitted to the Redlich-Kister type equation. The refractive index and density values of the mixtures were used to test the accuracy of some of the available refractive index mixing relationships in predicting the binary refractive index data. Viscosity results were also analyzed by using the McAllister four-body interaction model to correlate the kinematic viscosities of binary liquid mixtures.