Isobutyl isobutyrate is an important chemical which can be formed in a reactive extraction process with ionic liquid as dual solvent-catalyst. To design such an intensified process, the liquid-liquid equilibria (LLE) data for the esterification system involving ionic liquid are essential. In this work, the LLE of ternary systems {isobutyl isobutyrate (IBIBE) + isobutyric acid (IBAc) or isobutanol (IBOH) + 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIm][HSO4])} and the quinary system {IBAc + IBOH + IBIBE + H2O + [BMIm][HSO4]} were measured at temperature T= (298.2, 323.2 and 353.2) K, T= (323.2, 333.2, 343.2 and 353.2) K and atmospheric pressure, respectively. Based on the experimental data, the solute distribution coefficient and the selectivity were determined, which confirms the feasibility of the ionic liquid for isobutyl isobutyrate formation. The phase behaviour was explained by the molecular interaction using sigma-potential analysis. Moreover, the binary parameters of the NRTL model for [BMIm][HSO4] catalysed isobutyl isobutyrate formation system were fitted. (C) 2018 Elsevier Ltd.