New thermophysical properties are presented for the acetonitrile + water + butyl acetate ternary system and its binary constituents. Molar volume, molar refraction and isentropic compressibility changes of mixing were determined at 298.15 K and correlated with the Redlich-Kister polynomial. Isobaric vapour-liquid equilibria at 101.32 kPa were determined using a dynamic equilibrium apparatus. All systems verify the thermodynamic consistency and data were adequately correlated using Wilson, NRTL and UNIQUAC equations. Finally, the reliability of some group contribution methods, such as ASOG and UNIFAC, was tested by comparison with experimental results.