A Chemicals or organic compound that inhibitsthe oxidation of other molecules in biological system generally termed as Antioxidants. Upon oxidation of chemical compound produce free radicals, after chain of reactions that may damage cells. Either of natural or synthetic antioxidants such as ascorbic acid (vitamin C) or thiolsterminates terminates the chain reactions and prevents the oxidation of the molecules. Mainly two different groups of substances classified as “antioxidant" are:

1. Industrial chemicals that added to products for prevention of oxidation,
2. Natural chemicals added to food sand found in body tissue for beneficial health effects.

Early day’s research was going on the role of antioxidants which focused on the use in preventing the oxidation of natural unsaturated fats, to prevent rancidity. Simply by placing the fat in a closed container filled with oxygen, the rate of oxygen consumption is measured for calculating the Antioxidant activity. After the discovery of vitamins A, C, and E as antioxidants revolutionized the field of biochemistry that led to the realization of the importance of antioxidants in the living organisms. After identifying the process of lipid peroxidation and prevention of the peroxidation led to the recognition of vitamin Eas antioxidants. So Antioxidants are the reducing agents that prevent oxidative reactions, generally by scavenging reactive oxygen species so they cannot damage cells. In the present research comparatively studied the antioxidant activity of scallion and dry bulb of Allium cepa.