ABSTRACT: Mulla Sadra’s (c 1571-1640) commentary on Usul al-Kafi is one of the more famous commentaries on this significant Shi‘i hadith collection. For his philosophical and Sufi background, Sadra’s approach to the hadith is slightly different and in some ways contrary to the earlier commentators such as Allama Majlisi in Shi‘a and Ibn Taymiyya in Sunni Islam regarding the nature of Intellect. This paper aims to shed light on the way Sadra interprets al-Kafi and particularly to determine his understanding of the Aql (intellect) at the cosmic (as first created-being) and human levels as presented in the Kit?b al-Aql wa al-Jahl (The Book of Intellect and Ignorance). Sadra, already well-versed in the philosophical discourses on ontology and cosmology, finds al-KAFI as a fertile ground to develop and extend his vision of cosmos and existence. This paper, furthermore, investigates and reviews some later and contemporary scholars’ critiques of Sadra’s view on hadith and intellect.