ABSTRACTFree radicals are molecules containing one or more unpaired electrons in their outmost atomic or molecular orbital have emerged as double edged swords. current investigation showed that they can be both beneficial (e.g. required for normal physiological functioning) or deleterious (e.g. produce oxidative stress and responsible for various disease). Thus, it is important to understand all the aspects of free radicals while working in the this field.  The present review provides a brief overview on free radicals and their role in normal physiology,  oxidative stress, antioxidants and their evaluation. Keywords:  Free radicals, Antioxidant, Oxidative stress