As a result of exposure to radiation free radicals are produced in the body, few environmental pollutants and also as byproducts of metabolism. They can damage components of cell and result in various types diseases because of their highly reactive nature. Free radicals are neutralized by different types of systems in the body which include antioxidant enzymes like glutathione peroxidase, catalase, and superoxide dismutase and also small molecules of nutrient-derived antioxidant (vitamin C, flavonoids, vitamin E, carotenes, glutathione, taurine and uric acid). A delicate balance exists between antioxidants and free radicals in healthy individuals. In the present review different methods of antioxidant activity and their role in the management of different diseases have discussed. In some pathologic conditions like cancer and diabetes, the level of antioxidants falls below normal due to oxidative stress. Supplements of antioxidant for such conditions are expected to be beneficial. Regular consumption of antioxidant rich foods is the best preventive measure for certain diseases.