Ferroin is the chemical compound with the formula [Fe(o-phen)3]SO4 where o-phen is an abbreviation for 110-phenanthroline a bidentate ligand. The term ferroin is used loosely and includes salts of other anions such as chloride.

For R&D use onlynot for drug household or other uses.

Ferroin serves as an indicator of oxidation reduction reactionsin titrimetric analysis. Ferroin is the complex of 110-phenanthroline and Fe(II).[2]It is also used as a catalyst for BelousovZhabotinsky reaction.