Molar volume, isentropic compressibility, and molar refraction changes of mixing of the system diisopropyl ether (DIPE) + isopropyl alcohol (IPA) + water were determined at 298.15 K. These deviational properties were satisfactorily correlated with the composition data by means of Redlich-Kister polynomials. Tie line data have been determined at 298.15, 308.15, and 318.15 K for the ternary liquid-liquid equilibria, and were adequately correlated by means of the NRTL and UNIQUAC equation, and compared with results predicted by the UNIFAC method.