Nitronium tetrafluoroborate is an inorganic compound with formula NO2BF4.

It is a salt of nitronium cation and tetrafluoroborate anion.

[1] It is a colorless crystalline solid, which reacts with water to form the corrosive acids HF and HNO3.

Nitronium tetrafluoroborate can be prepared by adding a mixture of anhydrous hydrogen fluoride and boron trifluoride to a nitromethane solution of nitric acid or dinitrogen pentoxide.

[2] Nitronium tetrafluoroborate is used in organic synthesis as an electrophilic nitrating agent and a mild oxidant.