It is a tetrahedral molecule and is closely related to sulfuric acid, H2SO4, substituting a fluorine atom for one of the hydroxyl groups.

Reflecting its strong acidity, HSO3F dissolves almost all organic compounds that are even weak proton acceptors.

The self-ionization of fluorosulfonic acid also occurs: HSO3F isomerizes alkanes and catalyzes the alkylation of hydrocarbons with alkenes,[5] although it is unclear if such applications are of commercial importance.

[6] Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide:[2] Alternatively, KHF2 or CaF2 can be treated with oleum at 250 °C.

Once freed from HF by sweeping with an inert gas, HSO3F can be distilled in a glass apparatus.