Khwaja  Nasirudin al-Tusi is a versed scholar having occupied a very high position in the Muslim world. It is from his school that both Sunni and Shiite scholars have learned different knowledge. This article tries to study his intellectual theological project. Sheikh al-Tusi witnessed the Mongol occupation of the Islamic East and the devastating effects on Muslims and on their scientific and intellectual edifices at the time. This led him to make efforts to preserve what had remained of Islamic heritage. He also lived during a period of time that witnessed a wide critique against philosophical researching, besides the appearance of theological suspicions, which required him to deal with such accusations and suspicions by writing books and letters in addition to explaining the writings of others. In this context, he tried his best to establish a Twelver Shiite theology free from controversies, fallacies and nonsenses. In his theological approach, Sheikh al-Tusi sought to unite intellect and the Shariah, to show the Shiite beliefs in a logically systematic way, and to refute spurious arguments in a scientifically deductive way, until his scientific approach has become a compact reference to authors and scholars. This is what we will try to discuss in this paper and show the most important aspects of this approach.