Free radicals containing one or more unpaired electrons have considerable reactivity. Those radicals derived from oxygen represent the most important class of such species. Free radicals generated in organism are reactive oxygen species (ROS) and reactive nitrogen species (RNS) well recognised for playing a dual role as both deleterious and beneficial species. The cumulative production of ROS/RNS is termed oxidative stress and were discovered in pathomechanism of many of diseases. It was observed that in medium concentration ROS and RNS are play a role in inflammation, apoptosis and as secondary messengers in intracellular signalling cascades.