Khwāja Naṣīr al-Dīn Ṭūsī is among the influential sages and philosophers in the propagation of Islamic philosophy, and has left behind a vast corpus of works. Although many of his writings have already been edited and researched, certain philosophical treatises of his have not yet received the critical attention they deserve. One such treatise is “The Survival of the Soul after the Body’s Perishing.” In this work, Ṭūsī, drawing on the commonly accepted principles among Peripatetic philosophers - such as the materiality of the faculty of imagination and the denial of the Intermediate World (ʿālam al-mithāl) - attempts to prove the immortality of the rational soul (al-nafs al-nāṭiqah) after its separation from the material world. Ṭūsī’s views in this treatise are critically analyzed in the context of three main discussions. Among the issues open to discussion in his approach in this treatise are the incomplete argument regarding the non-immateriality of the faculty of imagination, the rejection of the intermediate world, and the ambiguity in explaining how the body serves as a condition for the soul. This treatise has been revised and edited based on seven manuscripts held in the libraries of the Astan Quds Razavi, Ayatollah Mar’ashi Najafi, the Islamic Consultative Assembly and Ayatollah Golpayegani library. Since the original manuscript was unavailable, a comparative method was employed in the reviewing process.