Al-Fadl ibn al-Rabi (, 757/8–823/4), was one of the most influential officials of the Abbasid Caliphate in the reigns of Harun al-Rashid () and al-Amin (), whom he served as chamberlain and chief minister. Fadl played an important role as the chief instigator of the civil war that erupted after Harun's death, siding with al-Amin against his half-brother al-Ma'mun (). After al-Ma'mun's victory he went into hiding, but eventually reconciled himself with the new ruler.