Ferrocenecarboxylic acid is the organoiron compound with the formula (C5H5)Fe(C5H4CO2H).

It can be prepared in two steps from ferrocene by acylation with a 2-chlorobenzoyl chloride followed by hydrolysis.

The acidity increases more than a thousand-fold, to pH 4.54 upon oxidation to the ferrocenium cation.

[3] By treatment with thionyl chloride, the carboxylic acid anhydride ([(C5H5)Fe(C5H4CO)]2O) is produced.

[4][5] Derivatives of ferrocenecarboxylic acid are components of some redox switches.