1-Butyl-3-methylimidazolium hexafluorophosphate, also known as BMIM-PF6, is a viscous, colourless, hydrophobic and non-water-soluble ionic liquid with a melting point[1] of -8 °C.

Together with 1-butyl-3-methylimidazolium tetrafluoroborate, BMIM-BF4, it is one of the most widely studied ionic liquids.

It may be obtained in two steps: BMIM-Cl is synthesized by alkylating 1-methylimidazole with 1-chlorobutane.

A metathesis reaction with potassium hexafluorophosphate gives the desired compound; the tetrafluoroborate may be prepared by analogously using potassium tetrafluoroborate.

BMIM-PF6 has been investigated in electrochemistry where it serves both as solvent and electrolyte.