This thesis dealt with issues of the creation of human acts, the kasb, and the istita'a in the Ibadhi and Mutazili thoughts from a comparative viewpoint. It consisted of an introduction, three chapters, and a conclusion. The first chapter studied the human action in both thoughts, starting with the historical dimension of the issue, and its development, then, it discussed the proofs of both groups, and showed aspects of agreement and difference between them. The second chapter was devoted to the concept of earning: kasb, so the study linguistically and terminologically defined the concept of earning, and demonstrated its implications in the Holy Quran and Sunnah, then it addressed the issue of historical origination of the earning statement and how it developed between the two parties, and focused on the proofs of the two parties and discussed the aspects of agreement and difference between them. The third chapter dealt with the issue of power: istita'a, then discussed its concept and semantic development and analyzed the proofs of both groups and highlighted the time of power and its validity. The study reached a set of results, the most prominent of which are: The term "the creation of acts" was not used by Mu'tazilites, because they attribute the action to God, hence this idea was created and propagated by their opponents. The Mu'tazila just proved man's responsibility in contradiction to the sayings of the Jabriyya, and they agree on this with the Ibadis. As for Ibadhis, the idea of the "creation of acts" was a response to the Mu'tazila and the Jabriyya. The thesis showed that there is no disagreement between the Ibadhis and the Mu'tazilites in the responsibility of the man over his actions except in rhetoric. Ibadi and Mu'tazilah agree that God Almighty made Man able to acquire his action, with a created capacity in him; and Man is responsible for the work he does, whether good or bad. Ibadi defined the gain in the idiomatic sense, so they expanded the concept, while Mu'tazilites remained with the linguistic perspective of the term. Al-Ibadiyah and most Mu'tazilites ج agreed that the ability is the health and safety of Man, while they differed regarding the survival of power and its suitability for the opposites. The study confirmed the existence of a convergence in inference to Istita'a in al-Ash'ari's Luma' and Basawi's Jami', so what we find both books is almost identica