Ammonium tetrafluoroborate (or ammonium fluoroborate) is an inorganic salt composed of the ammonium cation and the tetrafluoroborate anion, with the chemical formula NH<sub>4</sub>BF<sub>4</sub>. When heated to decomposition, ammonium tetrafluoroborate releases toxic fumes of hydrogen fluoride, nitrogen oxides, and ammonia.
Ammonium tetrafluoroborate can be prepared by reacting ammonium fluoride with boric and sulfuric acid: