Excess molar volumes, and changes of refractive indices, of the ternary mixture methyl acetate + methanol + 1-butanol, and the binary mixtures methyl acetate + 1-butanol, and methanol + 1-butanol have been evaluated from density, and refractive indices measurements at 298.15 K, and 1 atm. These derived properties of binary, and ternary mixtures were fitted to Redlich-Kister, and Cibulka type equations, respectively. The ERAS model interaction parameters of the binary systems contained in the ternary mixture were computed, the obtained results showing good accuracy. The high polar/associative behaviour of the mixtures should be the cause of high deviations in ternary excess prediction. The obtained results suggest the convenience of extending the model to multicomponent polar/associative mixtures in order to take into account all binary polar effects, and higher order polar effects in the mixtures.