Oxygen is one of the most important and indispensable elements, since life molecules on Earth can, under certain situations,produce from it constantly in the human bodytoxic molecules, called free radicals and/or other reactive oxygen species (ROS). ROS play a dual role in biological systems, since they can be either harmful or beneficial to living systems.These highly reactive species capable of wide spread, indiscriminate oxidation and peroxidation ofproteins, lipids and DNA which can lead to significant cellular damage and even tissue and/or organ failure. However, it is well known fact, thatmany of the ROS-mediated responses actually protect the cells against oxidative stress. On the other hand, over-production of ROS has the potential to cause damage. In addition currently some increasing evidence appeared showing that oxidative stress is associated with the pathogenesis of number diseases, likeneurodegenerative disorders,cardiovascular diseases,neuropsychiatric disorders, cancer, diabetes, cataract, etc.