In this work, liquid-liquid equilibrium (LLE) data for the water + propionic acid or butyric acid + mesityl oxide ternary systems were measured at (298.2 and 323.2) K under atmospheric pressure. The reliability of the experimental tie-line data was verified by the Othmer-Tobias and Hand equations. The distribution coefficient and selectivity, calculated from the LLE data, showed high efficiency for mesityl oxide extracting propionic or butyric acid from the aqueous solution. A comprehensive comparison with various other extractants not only confirmed the high extraction efficiency of mesityl oxide, but also revealed some general guide lines for further screening extractants for carboxylic acids. The experimental data were successfully correlated by both UNIQUAC and NRTL models, yielding binary interaction parameters for relevant process simulations. (C) 2017 Elsevier Ltd.