This research aims to mention how free radicals play a vital role in our body and gradually cause diabetes mellitus. According to studies, free radicals and oxidative stress play an essential role in the development of type 1and type 2 Diabetes. The human body is affected with diabetic Mellitus through beta-cell damage that may be the result of oxidative stress. As free radicals are highly reactive molecules including reactive oxygen species (ROS) and reactive nitrogen species (RNS). They disrupt the function of lipid, protein, DNA and the imbalance between them and antioxidants causes oxidative stress. Increased levels of oxidative stress in our body tissue and blood is considered to play a critical role in diabetes mellitus.