Isobaric vapor-liquid equilibrium (VLE) data for the methanol-methyl ethyl ketone (MEK) system containing 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM]PF₆) with varying mole fractions of 5%, 8%, 10% and 20% at 101.3kPa have been measured in a modified Othmer still. The VLE data were fitted with the NRTL model. The vapor-liquid equilibrium curves of methanol-MEK with [OMIM]PF₆deviate from that without [OMIM]PF₆. The azeotropic point disappeared when the mole fraction of [OMIM]PF₆was 8%, and higher mole fractions of [OMIM]PF₆ led to an increasing salt effect. The results show that [OMIM]PF₆ is a suitable solvent for extractive distillation of the methanol-MEK system.