Abstract: Cancer patients often use antioxidants with the aim of enhancing the benefits of treatment, alleviating side effects and/or maintaining or improving general health and well being. However, the use has generated controversy among onclogists some of whom are of the view that antioxidants by their very nature undermine the free radical mechanism of chemotherapy and radition therapy and therefore generally should be avoided during treatment. It is also known that in some situations antioxidants can act as prooxidants. Molecular modelling analyses of the antioxidants resveratrol, daidzein, coumestrol, lycopene, curcumin, gemistein, epigallocatechin-3-gallate (EGCG), indole-3-carbinol, sinalbin, sinigrin, folate, quercitrin, sulforaphane, silymarin, vitamin K1 and glucobrassicin that are known to possess chemopreventive properties, based on molecular mechanics, semi-empirical (PM3) and DFT (at B3LYP/6-31G* level) calculations show that the LUMO-HOMO energy differences for the compounds range from 2.1 to 5.9 eV, indicating that the compounds would vary significantly in their kinetic lability. The molecular surfaces of the compounds except sulforaphane and vitamin K1 are indeed found to abound in electron-rich regions in conformity with their protective role against oxidative damage of biomolecules such as nucleobases in DNA and cellular proteins and enzymes. The presence of significant electron-deficient regions on the molecular surfaces of sulforaphane and vitamin K1 and high reactivity of the molecules especially vitamin K1 may mean that the two compounds may be electrophilic in character so that they may cause damage to DNA and other biomolecules.