Like any other country, Iran has its own laws across constitutional law, civil law, criminal law, and the like. In Iran, Islam plays a central role in shaping social and legal principles. The practical manifestation of this influence relates to certain branches of the Islamic sciences that have specifically affected contemporary Iranian legislation. Sciences of Fiqh, Science of Usul al-fiqh and the science of qawāʿid al-fiqh are among the Islamic disciplines that occupy a special position in contemporary Iranian law and legislation. The question of this article — written in a descriptive-analytical method — is how and to what extent Islamic sciences influence the legislative system in Iran. This study demonstrates the hypothesis that Islamic sciences have formed the main framework for drafting laws, including the Constitution law, the Civil Code, and the Criminal Code. Despite the influence of Islamic sciences on modern Iranian legislation, the main contemporary challenge is the harmonization between Islamic sciences and the modern social and legal needs of Iran. The author argues that the future of legislation in Iran and influence of Islamic sciences on the legislative process will depend on the ability of jurists and legislators to interpret Islamic sources in a dynamic manner.