||Free radicals are molecules or molecular fragments containing one or more unpaired electrons. Oxidative stress occurs due to free radical generation and deficiency of antioxidant defence mechanism. Oxygen consumption inherent in cell growth leads to the generation of a series of reactive oxygen species (ROS). Oxidative damage caused by free radicals may be related to aging and diseases, such as atherosclerosis, diabetes, cancer and cirrhosis. The growing interest in the substitution of synthetic food antioxidants by natural ones has fostered research on vegetable sources and the screening of raw materials for identifying new antioxidants. Oxidation reactions are not an exclusive concern for the food industry, and antioxidants are widely needed to prevent deterioration of other oxidisable goods, such as cosmetics, pharmaceuticals and plastics. The aim of this review is to focus on the different in vitro and in vivo methods for evaluation of antioxidant activities.