Al-Fadl ibn al-Rabi (757/8–823/4) is one of the most influential officials of the Abbasid Caliphate in the reigns of Harun al-Rashid (reigned 786–809) and al-Amin (r. 809–813), whom he serves as chamberlain and chief minister.

Fadl plays an important role as the chief insitigator of the civil war that erupts after Harun's death, siding with al-Amin against his half-brother al-Ma'mun.

After al-Ma'mun's victory he goes into hiding, but eventually reconciles himself with the new ruler.