This study examines the concept of piety in Nahj al-Balaghah with a descriptive-analytical method. Piety is one of the most fundamental notions in the Nahj Albalagha. The analysis, here, is based on the separation of existential domains of human beings into three internal domains of beliefs, emotions, and desires, as well as two external domains of deeds and words. The concept of piety includes two components "fear" and "abstinence", the first of which belongs to the field of emotions and the second to the field of desires. Piety in the domain of emotion has levels of fear of punishment, apprehension of reward and fear of not being joined. In the domain of volition, also, piety includes the followings: the abstinence from sin, the prevention of damage, and the avoidance of negligence. The criterion for distinguishing these levels of piety within these two domains is the relation of human beings to God and the ways of knowing Him. The higher the levels of theology and anthropology, the higher the levels in which the piety will be realized. Another point is the mutual influence of piety in the domains of human existence. On the one hand, the piety in deeds and words is the result of the belief, emotions and intention; on the other hand, it can be effective in directing and enhancing the beliefs, emotions and desires.