Prenylation increases the bioactivity of flavonoids. Herein, we report the first examples of regioselective enzymatic geranylation of biflavonoids using Aspergillusterreus aromatic prenyltransferase (AtaPT). For biflavonoids 1–3 dimerized through a diphenyl linkage, geranylation occurs at the hydrogen bond involving C5′′–OH group, which is less chemically accessible than other OH groups in the molecule