Fluoroantimonic acid (systematically named fluoranium hexafluorostibanuide and fluoranium hexafluoridoantimonate(1-)) is an inorganic compound with the chemical formula  (also written , 2HF•SbF₅, or simply HF-SbF₅). It is an ionic liquid created by reacting hydrogen fluoride (HF) with antimony pentafluoride (SbF₅) in a  stoichiometric ratio of 2:1. It is the strongest known superacid, which has been demonstrated to protonate even hydrocarbons to afford carbocations and H₂. Similar acids can be created by using excess antimony pentafluoride.