This paper reports experimental data of density and refractive index for the binary systems of 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim][BF4], with 1,4-dioxane, and 1-ethyl-3-methylimidazolium tetrafluoroborate, [Emim][BF4], with 1,4-dioxane and ethylene glycol (EG). Moreover, for the system [Bmim][BF4] + EG we report here refractive index data. The measurements for the systems with EG were made over the entire composition range at atmospheric pressure (101 +/- 2 kPa) and in the temperature range from (293.15 to 353.15) K for densities and from (298.15 to 323.15) K for refractive indices. Because at room temperature the mixtures of both ionic liquids with 1,4-dioxane have indicated partial immiscibility, liquid-liquid phase equilibrium was determined. The excess molar volumes, V-E, and deviations in refractive index, Delta n, were calculated by using the measured experimental data and correlated by the Redlich-Kister type equations. V-E values are positive for the system with EG and negative for both systems with 1,4-dioxane, Delta n presenting an opposite sign. To probe the interactions in mixtures and to correlate the excess molar volumes of the mixtures the Prigogine-Flory-Patterson (PFP) theory has been used. Moreover, to correlate V-E and predict density and refractive index of the mixtures the Lorentz-Lorenz equation was applied.