Coumarins, an old class of compounds, are naturally occurring benzopyrene derivatives. A lot of coumarins have been identified from natural sources, especially green plants. These natural compounds have served as valuable leads for further design and synthesis of more active analogs. The pharmacological and biochemical properties and therapeutic applications of simple coumarins depend upon the pattern of substitution. Coumarins have attracted intense interest in recent years because of their diverse pharmacological properties. Among these properties, their antioxidant effects were extensively examined. In this review, plant derived coumarins and their synthetic analogs will be systematically evaluated based on their plant origin, structure-activity relationship and antioxidant efficacy. Owing their diverse effects and inconclusive results from different in vitro studies, the mechanism of their action has not yet been fully understood and the correlation of effects with chemical structure is not conclusive at the moment. It is the objective of this review will be to summarize experimental data for different coumarins used as antioxidant agents, because promising data have been reported for a series of these agents. In addition, their ability to bind metal ions represents an additional means of modulating their pharmacological responses.