Recent development in medicinal field reports a number of disease associated with free radicals. The risk of diseases due to oxidative stress is compounded by unhealthy lifestyle, exposure of chemicals, pollution, cigarette smoking, drugs, illness, and stress etc. Antioxidants are the substances which can scavenge free radicals and help to decrease the incidence of oxidative stress induced damage. Traditional herbal medicines, dietary foods were the main source of antioxidant for ancient peoples that protected them from the damage caused by free radicals. Over consumption of antioxidants however can cause severe adverse reactions as well. In this chapter we have discuss the concept of free radical biology and role of different antioxidants on human health and diseases.