The works and ideas of Shaykh al-Tusi, a renowned scholar in the Imami theological school and the head of the theological seminary in Baghdad, have always been influential and inspiring. His distinct viewpoint on human beings has profoundly shaped his ethical theory. This article employs a descriptive-analytical approach to explore the theological foundations and perspectives of Shaykh al-Tusi concerning the existential aspects of human beings and to clarify their impact on his ethical theory. Shaykh al-Tusi adopts a virtue based and deontological approach to ethical obligations, emphasizing the inherent nature (fitrah( and its role in ethics. He highlights the self-evident nature of innate moral judgments and propositions, giving priority to rational knowledge in this regard. This approach reflects a foundationalist framework in justification, acknowledging self-evident truths in theoretical and practical wisdom. Furthermore, Shaykh al-Tusi views adherence to innate propositions as the catalyst for moral flourishing and ethical development, indicating his inclination towards ethical realism and cognitivism.