Antioxidant activity of a molecule is attributed to various mechanisms such as prevention of chain initiation, binding of transition metal ion catalysts and decomposition of peroxides. This study was aimed at evaluating the metal chelating and hydrogen peroxide (H2O2) scavenging activity of melatonin. The metal chelating and H2O2 scavenging activity increased with increasing concentrations of melatonin (20–60 μg/mL). α-Tocopherol, butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT) were used as standards. Sixty micrograms per milliliter concentration of melatonin exhibited 95% chelating effect on ferrous ions and scavenged 83% of H2O2. On the other hand, the same concentration of α-tocopherol, BHA, and BHT exhibited 58, 61, and 72% inhibition, respectively, of the formation of the Fe2+–ferrozine complex and scavenged 48, 20, and 23%, respectively, of H2O2. Based on these results, it is concluded that melatonin is an effective metal chelating agent and scavenger of H2O2. These properties may be major reasons for the melatonin's ability to inhibit lipid peroxidation.