The reign of both Caliphs Abu Ja'far Al-Mansur and Al-Mahdi witnessed many crises resulting from the conflict over the positions of crown prince and caliphate, during which they dismissed some crown princes; so that the position of caliphate would continue in their sons and descendants. This resulted in serious consequences that sometimes led to murder. his research aims to monitor this phenomenon during the reign of the Abbasid Caliph Musa Al-Hadi (169-170 AH/785-786 AD), focusing on the relationship between his attempt to remove his brother Harun from the position of crown prince in favor of his young son Ja'far on the one hand, and the circumstances of his death on the other hand. Al-Mahdi had previously tried to put his son Harun ahead of Al-Hadi in the position of crown prince, under the influence of his wife, Khayzaran, but he did not succeed and fell victim to his attempt. At the end of Al-Hadi’s reign, he took the same path, and the state was divided between supporters and opponents. Harun almost agreed to give up his right to the crown prince position in favor of Ja'far, but the incitement of Al-Khayzaran and Yahya Al-Barmaki prevented that, so the situation went to the point of mutual threats of murder, which resulted in the killing of Caliph Al-Hadi and the assumption of the caliphate by his brother Harun Al-Rashid in 170AH/786 AD.