Isophthalaldehyde is an organic compound with the formula C<sub>6</sub>H<sub>4</sub>(CHO)<sub>2</sub>. It is one of three isomers of benzene dicarbaldehyde, a reduced analog of phthalic acid. It is a colorless solid, although commercial samples often appear yellowish. One preparation entails the Sommelet reaction of ñ,ñ'-diamino-ortho-xylene.
Like many benzaldehydes, isophthalaldehyde forms a variety of Schiff base derivatives. Being bifunctional (having two formyl groups), isophthalaldehyde allows the formation of polymers or covalent organic frameworks upon reaction with di- or triamines. They also find use in metal coordination complexes.