Although the issue of Imāmate was not initially seen as being one of the central subjects of Kalām, by the time it has gained importance especially after the Shīʿa started debating the matter in terms of credential aspects and as a result, it came to be covered as a specific chapter in Kalām books. The Muʿtazilite scholars on the other hand, did not lag from the relevant debates and included the matters that were related to Imāmate, in their works. Abū l-Ḥusayn al-Baṣrī who was portrayed among one of the most influential figures of late Muʿtazila and was also recognized as the founder of Ḥusayniyya branch within the school, wrote extensively on the subject at stake. From among his works, Imāmate chapter of Sharḥ al-Uṣūl al-Khamsa has managed to survive. Abū l-Ḥusayn al-Baṣrī’s work is crucial not only because it included Imāmate discussions prior to him, but also it determined the directions in which the relevant debates took place since many refutations were written against it. Considering that Baṣrī’s work reflects the issues of his time in terms of both content and classification, it plays a significant role in the development of Islamic political thought and Imāmate discussions. Including the debates on Imāmate, this work extensively discusses the rational defenses of 10th century Shite Imāmate theory. The only extant copy of al-Baṣrī’s work is preserved at Glaser collection from VI/XIII. century under the heading number 114 at the Austrian National Library in Vienna. This study provides an examination regarding the authorship of Imāmate fragment of Sharḥ al-Uṣūl al-Khamsa, analyses the main characteristics of the manuscript, its contents and its approach to the Imāmate discussions; and finally provides the critical edition of al-Baṣrī’s mentioned work to the attention of researchers.