Free radicals are generated in our body by several systems. A balance among free radicals and antioxidants is an important matter for appropriate physiological function. If free radicals become greater than the ability of the body to control them, a case known as oxidative stress appears, as a result of that, a number of human diseases spread in the body. Antioxidants can contribute to facingthis oxidative stress. The present review provides a brief overview of free radicals, oxidative stress, some natural antioxidants and the relationship between them.