Phytochemicals are now increasingly being used as nutritional supplements to either prevent or treat chronic diseases including cancer. The mechanisms of action of the phytochemicals can range from: inhibiting oxidative stress, apoptosis, inhibiting mitochondrial damage and inhibiting or promoting angiogenesis. The significance of oxidative stress in the etiology of aging and several chronic diseases: including cardiovascular disease, cancer and Alzheimer’s, has given support to the usage of these phytochemicals to inhibit oxidative damage. The complexity of the chemistry involved in oxidative stress damage to cells or tissue adds to the consideration of choice of the phytochemical to combat these effects. Cancer is a multifactorial disease. Epidemiological studies have shown beneficial effects of several phytochemicals in the prevention and treatment of several types of cancer. This chapter will address the role of oxidative stress in cancer and the antioxidant action of some of the most popularly used phytochemicals including-green tea, soy, resveratrol and ellagic acid (flavonoids, polyphenols).