4-Fluorobenzoic acid (p-fluorobenzoic acid) is an isomer of fluorobenzoic acid (FBA), an organic compound with the formula C<sub>7</sub>H<sub>5</sub>FO<sub>2</sub>. This colourless solid is a derivative of benzoic acid carboxylic acid. It is a synthetic intermediate.
4-Fluorobenzoic acid is commercially available. It may be prepared via the Schiemann reaction, in which a 4-aminobenzoic acid, protected as the ethyl ester, is diazotised and then fluoride introduced using tetrafluoroborate. Hydrolysis of the ester converts it back to the free acid.
4-Fluorobenzoic acid has been observed to form by the aerobic biotransformation of 4-fluorocinnamic acid.