The isobaric vapor-liquid equilibrium (VLE) data for the binary systems isobutyl alcohol + dimethyl sulfoxide (DMSO), isobutyl acetate + DMSO, and ternary system isobutyl alcohol + isobutyl acetate + DMSO were measured at 101.3 kPa. All of the binary VLE data passed Wisniaks modifed Herington area test and Wisniak point and area test. Ternary VLE data passed Wisniak point test. The VLE data of binary systems were correlated with NRTL, UNIQUAC, and Wilson models. The ternary VLE behavior were successfully predicted by the correlated binary parameters. The VLE data for the binary and ternary systems predicted by the correlated interaction parameters were in good agreement with all the experimental data. The relative volatility of isobutyl acetate to isobutyl alcohol can be greatly increased by DMSO and the azeotropic point of isobutyl acetate and isobutyl alcohol will disappear if the mole fraction of DMSO is greater than 0.36. DMSO is a promising solvent for separating the azeotrope of isobutyl alcohol and isobutyl acetate by extractive distillation.