The Abbasid State was founded by the descendants of Abbas ibn Abdulmuttalib. As in all the states by sultanate, the Abbasid State was also ruled by the descendants of Abbas. Although such a form of government seems to guarantee the same lineage administration of the satate, this management style has not been able to prevent debates and conflicts about the heirship. Because debates about the heir apparent began to emergence in the time of the first caliph Abu'lAbbas and caused serious porblems in later times. The person at the center of the discussions, both during the reign of Abu Ja'far al-Mansur and the Mahdi, was Isa ibn Musa. He was appointed as the second heir to throne by Abu'l-Abbas as-Saffah, but he had to leave the heir to the son of the caliph due to the pressure of Abu Jafar al-Mansur. During the reign of the Caliph Mahdi, he was forced to give up all his crown rights and died after a while. Isa ibn Musa, who was at the center of the heirship debates in the first period of the Abbasid state, is an important political figure. Having political and a military skills made Isa ibn Musa preffered. In this study, the position of Isa ibn Musa in the Abbasid administration will be tried to be revealed. In addition, an answer will be sought to the question of why he had to give up this right despite being the legal heir. In addition, the balance of power in the Abbasid dynasty and the effects these balances on the succession struggles will be emphasized.