In his early Imamate, Imam Kazem (PBUH) was facing challenges that caused his measures to be considered as actual evidence along with transmitted evidences. The main goals of this study are the reasons for Imam Mūsā bin Jaʿfar's imamate and the measures he took in proving this using the Shiite and Sunnite sources. The main question of the study is as follows: "What are the most important measures taken by Imam Kazem for proving his imamate in view of the evidences for his imamate in the Shiite and Sunnite sources?" This study was conducted in a "descriptive, analytical and comparative" method and found that for choosing an Imam, there are preconditions such as "testament, special knowledge, deposits, and age" as the criteria; and according to certain reasons, it is clarified that Imam Kazem enjoyed the preconditions for imamate. In addition to hadiths and transmitted evidences regarding his imamate, the most important measures he took were as follows: material and political stoicism, clarification regarding the usurpation of the Shiite right to government, scientific confrontation with deviated movements and various Shiite sects, debates with the Abbasid caliphs and adopting the reservation and religious dissimulation (taqiyya) approach. These show that Imam Kazem's mentality was that of "an authority, Imam and potentate", because he managed, on the one hand, the Shiite society through taqiyya and wikala (representation) and, on the other hand, he attempted to prove his rightness through various ways such as debates and bravery in stating the truths. He also struggled with the greatest challenge of his age scientifically and culturally, and established a conscious policy.