Polyphenols are one of the most abundant secondary metabolites in plants and as such are present in the human diet. These are low molecular weight chemical compounds composed of a three ring constitution with different supstituents. The plants use them as a protection against herbivore, infection, injury and they show a variety of antibacterial, antiviral, antioxidative, antitumor, anti-allergy, antimutagenesis and immunomodulatory properties and activities in animal organisms and in vitro. Because of all these properties they are in the last two decades the subject of many investigations, with emphasis on the antitumor activity. In this paper we have reflected only some of the polyphenols, their presence in animal organisms, their activity and potential clinical application. Antitumor activity in in vitro studies was shown for almost all used components, while in vivo investigations didn't show such a uniformity. The biggest obstacle is the limited biological availability. Therefore, it is assumed that the largest effect in the organism may have be done in the alimentary tract, because it is in direct contact with the oral applicated polyphenols, which is actually the goal of such research, to demonstrate effective inhibition of growth and development of tumors using natural components of food.