Densities, viscosities, and refractive indices for binary and ternary mixtures of ethanol, ethyl acetate, and 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide have been determined at 298.15 K and atmospheric pressure. Excess molar volumes, and viscosity and molar refraction changes of mixing have been calculated from the measured physical properties. These changes of mixing have been adequately fitted to the Redlich-Kister polynomial equation. The adjustable parameters and the standard deviations between experimental and calculated values are reported.