One of the most important principles of criminal jurisprudence is the legal maxim Actus Non Facit Reum Nisi Mens Sit Rea, which highlights the requirement of guilty mind in addition to a wrongful act in order to establish criminal liability. The maxim expresses the idea that an act alone cannot make a person criminally responsible unless it is performed with a blameworthy state of mind. This article examines the meaning and significance of the maxim, its historical development, and its application in criminal law. It further explains the essential elements of crime- Actus Reus and Mens Rea- and discusses situation where the requirement of Mens rea may not apply. The paper also analysis relevant judicial decisions to demonstrate how courts apply this principle.