No doubt that most of Islamic Sciences in their genesis and development have been indebted to the narratives of the infallibles (maasumin). But many believe that nearly all of the debates in Usul- Fiqh (an Islamic science) have been obtained from other Islamic sciences and the rules of this science are based on Reason, Custom, philology and the way of acting of the wise men (sire Oqala or practical tradition). The present paper states that Hadith in Shiism is dealt with in Usul Fiqh and also it has a particular status in elicitation of some of the fundamental rules for deep understanding of religious texts. It is also noted that Hadith in science of Usul Fiqh of Shiism has an important role as to the validation and authority.